There is no store to buy things like that on this forum. You will be able to change your user title when you reach 1000 posts (and it'll change periodically prior to that. You are free to add things to your signature as long as they're within forum guidelines--big signature pictures make it much harder to load pages for those on dial-up or smartphones, so we want to keep them fairly small.
Sorry for such a long delay in the answer.
From MST3K's spoof of "Hercules Unchained"--heard as Roman medic soldiers carry off an unconscious Greek Hercules on a 1950's Army green canvas stretcher: "Hi, we're IX-I-I. Did somebody dial IX-I-I?"