Well, you can't use IDs, because you are using those for coordinates.
And in any case if you use that map generator based on the letters, as you are doing now, how would you piggyback an indicator on top of one of the letters?
Honestly, likely the best way is exactly as I described in post #43. Put them in a separate array, like that, using their coordinates. Is that viable for you??
An optimist sees the glass as half full.
A pessimist sees the glass as half empty.
A realist drinks it no matter how much there is.