The concept of "Mr." as a title of address before a man's name is an
aspect of English Language.
It is simply not a common part of ASL.
If for whatever reason you feel you need to express the concept of
"Mr." just spell it. (Don't add the period. And don't do it
near the forehead. Just spell it in the normal fingerspelling
See: "Titles of
Also see: "Name Signs"
You can learn
American Sign Language (ASL) online at American Sign Language University ™
ASL resources by Lifeprint.com © Dr. William Vicars