So unless he broadcast it, how would people know? My Dad, brothers, son, nephews all carry one.
As you implied, it is going to be hard. In the suspect's favor, he could point to his Eagle scout rank to support a claim that he routinely carried one. The connection between Eagle Scout and routine knife carry is reasonable.
A possible counter argument by the proscecution could be when the knife was purchased. If it was purchased just prior to the rendezvous and especially if the suspect went out of his way to purchase it, a claim of "Well, I always carry one and just needed one." would be harder to support.