Is there a quick way to determine if a character string represents a legal numeric string (contains only digits and maybe a sign or .)?

I've tried using type(),vartype() and evaluate(), but they don't give me quite the right thing.

Suppose I have a variable NorC.

If it contains the string '1.2' I want mytypefunc(NorC) to return 'N'
If it contains the string 'A.1' or '1.A' I want mytypefunc(NorC) to return 'C'

EVALUATE('NorC') returns a character string in both cases.
EVALUATE(NorC) returns a numeric value in 1st case but gives an error in the second case.

Combinations of vartype(),type() and evaluate() do not give what I want.