Is it possible to require cells to only allow 1 letter?

[mollyw820]

I am looking for a formula (if it exists) where I enter a 15 digit code, starting with W (ex: W12345678901234) and the cell will only except the code if it starts with the letter W, so if X12345678901234 is entered into the cell it would provide an error message.  Is this possible?

[#2]

@mollyw820 

=LEFT(D3,1)="W"

You can try this rule for data validation of cell D3.