This is an interesting subject.
I say that because last week they were talking about this on Radio 2, on the Jeremy Vine Show I think.
They explained all about Trig Points, their origins etc with an expert who phoned in.
They also said that a few years ago the government auctioned them all off, thus letting members of the public have a chance to 'adopt' one of them, and have a record of 'ownership'.
If I'm honest I've never heard of them before.
Also, looking through all the pictures and posts I've noticed that someone has posted a Trig Point literally just a stone's throw from where I live!
Now that I know there's one in my vicinity I might go and look for it...