Robot mode: on character page. click upgrade. select robot mode at bottom.
Alt modes: Are on a rotating cycle every 2(?) they cycle around some leaving and some staying. All the groups have fairly different lists with some overlap. Also some people have alt modes that they won in a terny or used to be in the list and they have never reset. Just wait. But don't worry about the alt mode right now all of them will be reset when the final pieces of V.2 go online.
Factions: The preds and Maxis in the game are to test out the code dealing with 4 factions and to my knowledge no more will be transfered over until the start of V2 when everyone will get the chance to choose thier faction again.
About the sig. There is a way of getting pics in it but you have to get an off site host for the pic. Check out the ask the experts forum here for more info.
Also

doesn't help you get your point across.