How can you tell Indian scripts apart without knowing the languages?

By silhouette. Ask three questions in order: is there a continuous horizontal line running along the top of the words, are the letterforms dominated by circles and loops, and does the text sit in a squarish block or a rounded one. Those three answers separate most of the major Indian scripts without reading a single character.

What is the horizontal line on top of Hindi writing?

It is called the shirorekha, and it runs continuously across the top of each word in Devanagari, joining the letters. It is the fastest script read in India: present means Devanagari, which means Hindi, Marathi, Nepali or several other northern languages. Gujarati uses nearly the same letterforms with the bar removed.

How do you tell Telugu and Kannada apart?

They descend from the same script and are genuinely difficult at Street View resolution. Telugu letters tend to carry a small curved tick or hook above them and read as slightly more separated; Kannada letterforms are typically rounder and more closed. In practice most players resolve it with context instead: Telugu means Andhra Pradesh or Telangana, Kannada means Karnataka, and terrain, plate codes and city names settle it faster than the letterforms will.

Which Indian states do not use an Indic script on signs?

Nagaland, Mizoram and Meghalaya use English as the official language, so their signage is frequently in the Latin alphabet only. In a country where almost every sign carries an Indic script somewhere, an all-Latin street scene is a strong North East signal.

Reading Indian Scripts: Which State Uses Which Alphabet

You do not need to read the words. Ten scripts, told apart by shape alone, and each one maps to a small handful of Indian states. Includes the confusion pairs and why the Hindi belt defeats this method.

You are not trying to read the sign. You are trying to recognise its shape.

India uses about a dozen scripts in daily official use, and each belongs to a small number of states. Script identification is a visual task, not a linguistic one — you can do it reliably without knowing a single word in any of these languages.

The three questions

Look at any block of non-Latin text and ask these in order.

Is there a continuous line along the top of the words? If yes, you are looking at Devanagari or Bengali-Assamese. That one question splits the country roughly in half.
Is the text dominated by circles, loops and curves? Malayalam, Odia, Kannada and Telugu are round scripts. Devanagari and Gurmukhi are angular.
Does each character sit apart, or do they join? Tamil reads as separate, open forms with few stacked pieces. Most other Indic scripts stack marks above and below.

The scripts, by silhouette

Devanagari: A continuous horizontal bar — the shirorekha — across the top of every word, with angular forms hanging beneath it. Hindi, Marathi, Nepali, Konkani. The single most common script in India and the least useful one.
Gujarati: Devanagari with the top bar deleted. The letterforms are close cousins; the missing bar is the whole difference. Gujarat.
Gurmukhi: Also has a top bar, but with far simpler, more open, more angular letters than Devanagari and a distinctly sparse look. Punjab.
Bengali-Assamese: A top bar again, but the forms below it are curvier and more triangular than Devanagari, and often look like they are leaning. West Bengal, Assam, Tripura.
Odia: Unmistakable. Almost every character is topped with a bold curved umbrella, so a line of Odia reads as a row of domes. Odisha.
Tamil: Open, rounded, widely spaced, with very little stacking above or below the line. Looks calmer and less dense than its neighbours. Tamil Nadu, Puducherry.
Malayalam: The roundest script in India — tight loops and curls, visually busy, no top bar. Kerala, Lakshadweep.
Telugu: Round and looping, with small curved ticks riding above many characters. Andhra Pradesh, Telangana.
Kannada: Round and looping like Telugu, generally more closed and more compact. Karnataka.
Perso-Arabic: Flowing right-to-left cursive. On Indian signage this points at Jammu & Kashmir, or at older signage and Urdu-language boards elsewhere.

What each script is worth

Script	States	Value
Malayalam	Kerala	Round essentially over
Odia	Odisha	Round essentially over
Gurmukhi	Punjab	Round essentially over
Gujarati	Gujarat	Round essentially over
Tamil	Tamil Nadu, Puducherry	Near-decisive
Kannada	Karnataka	Near-decisive
Telugu	Andhra Pradesh, Telangana	Two candidates
Bengali-Assamese	West Bengal, Assam, Tripura	Three candidates
Latin only	Nagaland, Mizoram, Meghalaya	Strong North East signal
Devanagari	Ten-plus states	Rules out the south only

The confusion pairs

Three pairs cause almost all the mistakes.

Telugu vs Kannada: Same ancestor, similar rhythm, and at sign resolution they blur together. Do not burn the round on the letterforms — check plate codes and terrain instead. Karnataka gives you the Deccan plateau and Bengaluru; the Telugu states give you the coastal Andhra delta or the Hyderabad region.
Devanagari vs Gujarati: Identical family, and the only reliable difference is the top bar. If you cannot see whether the bar is there, you cannot separate them — find a longer sign.
Bengali vs Assamese: Effectively the same script with a couple of extra letters in Assamese. Separate them with geography, not type: Assam is tea gardens, hills and the Brahmaputra valley; West Bengal is delta, paddy and far denser settlement.

The Devanagari problem

Roughly half of India writes in Devanagari, so recognising it correctly still leaves you with a region the size of Western Europe: Uttar Pradesh, Madhya Pradesh, Bihar, Rajasthan, Haryana, Himachal Pradesh, Uttarakhand, Delhi, Chhattisgarh, Jharkhand and Maharashtra.

Devanagari is not an answer. It is the point at which you switch to other evidence.

When you land on Devanagari, stop reading signs and go to plates, terrain and construction — the approach set out in the India pillar guide.

Reading the signs you actually get

Official signage in India is usually trilingual — the state language, Hindi and English — which is generous, because the state language is the one you want and it is generally printed first or largest.

Government boards and milestones follow the state convention most strictly. Best source.
Shop and hoarding text is the most abundant, and often the state language alone.
Bus destination boards carry both the script and a town name in English on the same panel — the best two-for-one in an Indian frame.
Political posters and wall paint are everywhere in India and are almost always in the local language.

And when a sign gives you an English town name alongside the script, take the town name. It ends the round, and no amount of letterform analysis beats that.

Reading Indian scripts: which state uses which alphabet

The short version