It is no argument to claim that something doesn't exist because a handful of people "haven't seen it" - you would be laughed out of any court in the land
That is only because it is very difficult (if not impossible) to prove a negative.
However, you could prove that these signs are 'common in Britain' if you could provide details of where they may currently be seen.
Proving a positive is much easier, but you consistently fail to do so, relying on historic and/or anecdotal evidence (which is no evidence of the current situation)