Again, not legal advice here but my opinion...

If to a reasonable person your icons appear to be based on the TSR set then they could be deemed as derivative in which case you would be in breech of copyright. TSRs symbols presumably were not trademarked or registered for that purpose. If you can find those symbols in maps prior to those used in the first TSR maps then your ok with TSR and maybe not ok with the prior creator. If just one or two are similar but not exact and the rest are different then its likely that you would get away with that on the grounds that it was coincidental. Like two books using the word "and" - it just wouldn't wash at all. Or if the symbol is so general or obvious then you could argue that TSR never made any creative input into it anyway. But if as your saying that you studied the symbols and made a similar set then your not really in the clear.

I don't know your product well but you could try to contact them and get an ok on it cos they just might not care. Or else they might want a cut on a sale price for the symbol use. All said and done it usually follows the path of most profit so if they are not making any money form these symbols themselves any more then they might not care. If they are and think it will harm their trade then they might well care.

Ultimately, if Wizards (who I thought bought out TSR) started suing everyone in the area of their game then the fan base might collapse. TSR used to be known as "They Sue Regularly" and they didn't win any friends. A lot of people moved away from them as a result. I think Wizards have done much better with the OGL and so on.

They have to get more people playing with their products not sue the fans for a few bucks - unlike the music industry for example - so as you can see, nothing is black and white.