By default there no signature template at Blogger, correct me if I wrong :D. So, I must make it "manually" when I post something to Blogger. I have idea to make it using post template feature at Blogger. You can find this by go to Settings > Formatting > and you will get Post Template form (last form I think) :D
"Post templates help users save time by pre-formatting the post editor. " -- from Blogger Help.
You can fill that form which your signature. I put my image signature called my userbar and I think it's so cool Hehehehe....