The longer answer is that you possibly can recognise a witch but it is pretty tricky. The trick to spotting a practising witch is firstly to free your mind of preconceptions. Obviously a witch doesn’t look like the various Disney interpretations but nor is she/he particularly old, beautiful, warty, mystical or liable to break into a cackle at short notice. The average witch doesn’t dress differently to other people and ostensibly to the outside world he/she doesn’t do anything different to other people.
This can be hard to grasp. Witches are still viewed with the approach that the word “witch” describes what they are rather than what they do. This does lead to the misconception that they look and behave in certain ways. What you have to remember when looking for witches is that witch is a descriptor of what they do, they practise witchcraft. So what you need to look for are the signs of the practise itself rather than the stereotypical features of those who practise it.
I’d say you’d get your best evidence from being in the home of the witch. That isn’t to say that the home will be lavishly decorated with items from Nemesis Now (though to be fair I’d say most witches won’t be able to resist the occasional ornamental nod to their craft) but do look for the functionality of items that suggest a craft path is being followed. It isn’t stereotyping to say that most witches will have a cooking pot used for modern cauldron purposes. She’s likely to have bottles, herbs, incense, candles and oils lying around the place. You may also see interesting little personal collections of feathers and stones, innocuous enough in any home but when all added together suggest a clue that a witch may be present.
If the witch is private about her craft her public bookshelf probably won’t have her personal collection of craft related books on display. But large chests, locked cupboards and (my favourite) very random dust jackets hiding completely different books underneath may all be good indications you are in the home of a witch.
Recognising a witch outside her primary environment is harder. A competent witch is well versed in the art of hiding in plain sight. However he/she may display interest (and knowledge) in areas linked to witchcraft. The witch is unlikely to pipe up to get involved in discussions on the craft itself but she/he may be the person in the office who always knows when the next full moon is or always knows which natural remedy to suggest for various ailments. Look again for the craft practises being incorporated into daily life.
Certain things in the workplace can also offer clues. I’ll give you a few examples. I’m in my mortgage office now which to the outside world looks like any other mortgage office until you take a bit of a closer look. Firstly there is a very fine line of salt that blocks the office from the outside world. Faint, you’d have to really look to notice it. In the cupboard next to my cleaning spray is another spray. If you sprayed it and sniffed you’d recognise certain scents including lavender. That’s a spray to change the aura of the room. On the desk I have a piece of amethyst and in the drawer there is an unlabelled oil blend in a small jar. Any one of these things could easily be explained away and even all combined would only be a clue to somebody who knew what they were looking for. But subtle changes like these in the environment around a person may suggest he/she is a practising witch.
In summary, trying to find a witch on the basis that they are a witch is well nigh close to impossible. There is no personality type or “look” that can be linked to a practising witch. The only real chance you have is finding evidence not of what they are but of what they do and this is best achieved by looking for the signs of the craft that they practise.