Did Mest have a guild mark?
No, Mest Gryder did not have a Fairy Tail Guild mark. And neither did he need one. As his ability which allowed him to infiltrate to begin with can also cover for the lack of a guild mark. Allowing him to be a Fairy Tail member, without a Fairy Tail mark.


  Doranbolt, a member of the Magic councel, used Memory Control to deceive everyone in Fairy Tail into believing he was a member of their guild named Mest Gryder.


Edit

Is it a speculation? Mainly yes but do consider the following. His power allows him to make everybody think he is a guild member. To obtain a real guild emblem he would need to go to Makarov and ask for one. Which at that time already should think that he is a member of fairy tail. Which would make it weird for him to ask for a guild mark.