By disabling the signature they can only stop viewing the signature from their account for them as well as other users but anyone can still see their signatures/avatar if they are wearing one and hiding signatures in the display option will not affect how others see their profile.

And if they want others to stop their signature, then it should be blank.

The actual reason why many don't see is due to using AdBlock extensions, which also hide the signatures from bitcointalk if I am not wrong.