I'm afraid they'll need further "diet" ihihih
Since I'm a total n00b of this forum I was checking right now the forum rules... and about images in sigs:
Most of them, being 90px tall and having a "weight" of +30KB, exceed both constraints (both height and file-size)
Nforcer is right. Everything that we made can be adjusted to fit
Here's an example:

289 x 65, 20.6kb