GREAT shot, Drew! Good thing, too as those bridges' days are numbered. Speaking of numbers, Margaret, the plates are not mileposts. These signals are Intermediate Signals, so indicated by number plates below the signal. In this case, you have signal 1983 and signal 1985. That indicates each signal being close to milepost 198. The 3 and 5 indicate a westbound protecting signal, as eastbound would have even numbers. Eastbound signals near here might have number plates 1982 and 1984. Next time you're trackside, take a look at the number plates, and note that there are never decimals, and signals are ususally close to a milepost, but seldom right at a milepost.

I don't know how the SP/UP designates their main line tracks through here, but if I had to guess signal 1985 is MT1 or North main, while 1983 is above MT2.