Lolwut, no!?
It makes sense from a purely technical perspective, but it really does not seem to have any logic behind it.
Why are they collapsed if they're turned on for non-donators? Those are the people who need to be seeing the signatures the most, especially Grazr's and Booj's which are so damn incredibly useful.
Honestly, unless a good honest reason can be provided as to why there is even this default signature blocking in the first place, just scrap the system. Seriously.
If it's just a case of "Oh look what I coded, a dropdown hider thing, I must keep it in some way", get rid of it.
If it's a case of "Oh, some members don't want to see signatures", let them have the option to turn them off / hide them.
New people who may not realise how useful the signatures can be are never going to turn them on out of usefulness - just maybe out of slight curiosity. If they're shown the signatures and don't want any of it, fine, they can be hidden. But if they never realised signatures could be hidden if they're on by default in the first place, are they honestly going to complain? "Oh no this guy's anime signature has broken my immersion of this TF2 website"
TL,DR: Hiding signatures by default has no benefits and only serves to make new members miss some important information contained within them (ABS' Pack, Grazr's tutorials, DJive's Mapping FAQ)