A suggestion would be to have a sightings forum, for instance I saw a nice red V6 with the Eleanor grill, side scoops and at least an axle-back this morning and though it might be someone who is a member here since it's modified.

A forum where we could post to see if they are a member here, they had this on another forum I use to belong to (not a Mustang forum) and it worked out well.

 

Not a bad idea, but in most cases people would have just asked in the regional section if the car belonged to a member.