Find if value exists using SQL True/False Return
This code is open to injection. Consider
what happens if I pass sometext'; Drop Table TblTable; -- into
that variable. Use a proper parameterized query instead.
The SQL statement itself is about as efficient as it can be to my
knowledge. A count would add extra overhead. Using an Exists might
garner you a negligible amount of performance at the cost of
readability. (Exists wouldn't need to return any value at all
except what you tell it.)
You could simplify your return statement by using IsNullOrEmpty()


Instead of:

                If result = "" Then
                    Return False
                Else
                    Return True
                End If


You could just use this:

Return Not String.IsNullOrEmpty(result)