Club tags and allowed characters

So, trying to figure out exactly what character's are allowed in club's tags. A lot of the tags I've attempted to make have been declined because the tag "does not meet the requirements". A 4 character tag that "does not meet the requirements" can only contain illegal characters.

Now here's where my confusion sets in. At first, I assumed maybe it was only the base Ascii printing set that was allowed. Ascii 33-126. Essentially, anything that a standard, American, QWERTY keyboard is capable of typing with no more than 1 key + shift. I tried the Extende Ascii set, Ascii 128-255, which it seems that the majority of these characters are not allowed.

And then I saw the ™ symbol in a tag.

™ is not in base Ascii set. It's not even in the Extended Ascii set. In fact, it's unicode value is U+2122 (note that this is actually 8482, because unicode is in hexadecimal/base16) Now... It's not that all unicode characters up to and including U+2122 are usable. I've tried Ï (U+00CF, Ascii 216), and it didn't work.

I haven't found anywhere that gives a comprehensive list of what characters and symbols are actually allowed, and I hardly want to go through a list to see just what ones aren't available, just to accidentally find a random character that is allowed, and have to re-create my club.

Can anyone, Red or not, give me a list of all characters allowed in a club tag? And perhaps a Red to explain why the Extended Ascii set isn't available for use?