[Tagging] Route Relations and Special (Bannered) Routes

[Nathan Edgars II]

It's obvious to me that the "banner" is not part of the network. US 1 
Alternate is part of the U.S. Highway system (US:US), not some mythical 
"U.S. Highway Alternate" system.

It also makes the most sense to put it in the ref tag. Otherwise there's 
inconsistency between an alternate signed as US 1 Alternate and one 
signed as US 1A (with the suffix in the shield). In each case I'll also 
use the modifier tag (modifier=Alternate/A).