They look at you when they think you are busy

Somebody looking at you while you are occupied is the least deliberate thing on this whole list. They did it believing nobody was watching them do it, which is exactly why it is worth more than anything they have said out loud.

How to read it

Attention goes where a mind already is. When you are busy — working, reading, talking to somebody else — there is no social reason to look at you. Nothing is being performed and nobody is being polite. That is what makes this the hardest signal to fake and the easiest one to believe.

What matters is repetition, not intensity. One glance is nothing, because everybody's eyes wander. Three separate times in a week, in different rooms, is a pattern, and this entire question is made of patterns.

When it means nothing

It means nothing if you are the only moving thing in a dull room. People look at doors, at movement, at whoever just laughed. If it only ever happens in one setting, you may be reading the room rather than the person. It also means very little on its own — attention with none of the other signals attached is usually curiosity, and curiosity fades on its own.

Your move

Do not turn around and catch them at it. Notice instead whether it survives a change of room. If it does, you have your evidence, and the next move is yours to make rather than theirs to confess.