Why is it a bad sign if you find a piece of transparent tape stuck on the lock of your front door?

It's a trick of burglars ...

They put a piece of tape on the lock of a house or apartment and go back one (or more) day (s) after, to see if the tape is still intact.

If the tape is not pierced or has not been removed, it means that there is no one in the accommodation.

And so, that it is possible to burglarize it without being disturbed ...