AVI is just a container format. You'd have to get the specifics from the sign folks on what video format is allowed inside that container with regard to codecs, resolutions, frame rates, pixel aspect ratios, bitrates, etc. Once you have that information, you'll know what to do.
OMG! I finally got the sign company's phone number and called their tech support and he was clueless! He didn't even know what a codec was!
All he knew was that the frame rate is 30, pixel matrix is 48 pixels high by 96 pixels wide, and WMV is actually a preferable format to AVI.
But I see WMV also isn't an option in Premiere, so I'm guessing that is also nothing but another container?
Maybe I should just export it to Quicktime and find some free translation software to change it to WMV.
WMV is more than just a container like AVI, it's an actual codec. Both are available on Windows version of PP, neither are available on the Mac version.