What does this mean?

What is the meaning of the symbol, consisting of a question mark inside of a black diamond shape?

Currently seen where opening comment truncated under heading for Town Centres' thread, but nowhere else on this page.

Hi Ena,
I did a search and there are several explanations but it appears to be a replacement for as character that doesn't exist within a particular font.
The general explanation I found is this:
"The replacement character , a black diamond with a white question mark, is a symbol found in the Unicode standard at codepoint U+FFFD in the Specials table. It is used to replace an unknown or unrepresentable character, or indicate problems when a system is not able to render a stream of data to a correct symbol."
Hope this helps.

But the next character in your opening post is an apostrophe ( ' ). and we can clearly see in a thread further down. (entitled: This can't be for real) that an apostrophe can be shown. The font used when we enter stuff is not a thing we can change, is it.

Since the site software was upgraded, yoo cannot post characters from the character map, into post headings and the posting body, I don't know if that is for all characters, but certainly for ones I have tried such has the musical symbols, and that apostrophe in question, for some reason is a different type of apostrophe, from the standard font, maybe from a different font, which JR used when posting it, and it must have been identified by the site software has being a 'naughty' apostrophe, and a not allowed character, hence the forum software has refused to publish it

Yes, I also have had the experience of not being able to post music symbols, etc.

I guess it is always possible that JR's post was C&P, and the original being in a font that baulked. Otherwise, we type into the box, as I am currently doing with this comment, That is, it is WW not me that is allocating a font to my input.

Ena

I suppose that is possible, because I cannot find an apostrophe like the one which JR posted and the software has allowed it to be posted in the post replies, but not in the post topic box.