The poster you are referring to now says he wasn't interested in knowing your number plate but had one for sale, sounds even more iffy to me.
The damage can be considerable if you get caught up in someone cloning your number plate. The legwork involved talking to various agencies trying to convince them its not you. They must hear that excuse a dozen times a day. Garages and the like are now becoming very aware of cars with reg plates on as they now cover them up. It's a minor thing to do but could save you an awful lot of heartache and trouble.
About 30 years ago I owned a Ford Granada Estate, lovely car, I won't put the reg number up here as it is still in use today. Police at my front door 11 pm asking if it was my car, I, of course, said yes and I was immediately arrested for the theft of a horse trailer. I went off with them and they checked the tow bar on my car which I had never used. It had a plastic cover and they tried to get this cap off but couldn't, they radioed for another copper to attend who they said would get the cap off. He arrived but could get it off. So they dearrested me and asked me to attend their police headquarters the following day. This I did They asked me where was I the day before at 5.30am? I told them in bed with the wife they went out and asked her the same question. Eventually, they had to accept what I was telling them and let me go. They did some months later find the people who were using other peoples reg and thieving fortunes, speeding and parking tickets etc. I know our plates are always on display but they do for some reason like plates on cars being transported etc.