Mimi has designed most of the signature pictures that the members have. She is a graphics design artist, and a pretty awesome one at that. Most of the time, if she has the time, she will design members signature pictures for themselves, and often changes her own as well.
My advice, if you would like one, private message her and discuss it with her. Usually, if she has the time, she is happy to help, and she can probably work with you on whatever signature you want. Whatever is it you want, trust me, it will come out great.
Hope that helped.
Mitch