Animations far as I know are only done in photoshop here is a link discribeing how to do them.
http://www.myjanee.com/tuts/animation/animation.htm

To make it flash like romeo's. All you need to do is 2 tags and follow the directions in the link above and just make 2 frames. One with the starting image followed by the second image. You can adjust the delay in the last step before you save the file as animation by adjusting the "seconds delay" something like .5 or .7 should do the trick.

Something link my signature takes upwards of 36+ frames to create that dancing yoda.

You can also get creative and use a step fading into the second picture from the first and set that up as an animation. but that would take a minimum of 10 frames per fade in and out for a grand total of 40 frames for a 2 picture signature. It's alot of work but looks REALLY nice when you finish it.