You can have as many animations as you want if they don't all in total exceed 300 pixels in height and 500 pixels in width, I do believe. I haven't found a rule otherwise. @@
To find out, you can right-click on each animation, and click "element properties" (well, that's what it is on Firefox). It'll tell you the height and width.
Also, if you have a sig with a ton of images, make sure that there isn't alot of text or uneeded spaces. The more text you have, the longer it is and the higher the chances that a staff member may feel that an edit is in order. :/