Delete or Rename first solo Character in directory

I´ve no idea how i can rename only directorys named with a single character like

"A" into "#A#" Directorys like "Adams" should be untouched.

Thanks for our Ideas

Replace: "^(.)$"
With: "#\1#"
Use regular expressions

This will rename any single character as you specified.

"^" & "$" specify the beginning and the end of the string respectively.

Reply to #2:
gorgeous! Works perfectly -thanks. Saves me a lot of Handwork.