61/14 or 14/61?

The major highway through this town is a concurrency of U.S. Route 14 and U.S. Route 61. Some of the signage looks like this:

U.S. 61 route shieldU.S. 14 route shield

And some of the signage looks like this:

U.S. 14 route shieldU.S. 61 route shield

I still haven’t figured out what determines the order of the route shields.

(Route shields by Wikipedia user SPUI: 14 source, 61 source.)