It's pretty difficult to pin down the exact ID of the typeface used for "BAR." It could be an extra-bold variant of Avant Garde or something else. Certain typefaces, such as Futura, have numerous variants from different companies (Adobe, Bitstream, Neufville Digital, etc). None of them are the same! They're all slightly different in various ways, different enough where a replacement face will not line up with the existing letter return properly. You have to have the original art files or you're forced to create a paper pattern and make letter face replacements from that.
Another hazard with channel letter faces: way too often you'll have some hack who created the original sign layout squeeze or stretch the typeface out of its normal proportions. So even if the typeface in question is very obvious you end up having to create a paper pattern from the sign anyway. I personally hate distorted type on signs; it's one of the fastest ways to make a sign design look completely unprofessional.