We were VIking-2 in Lawrence until around that same time.
We had "RH" - but it's not in the AT&T list that the article points to, and it has no obvious georeferent. RHode island was the wrong state, RHodesia was suboptimal, and RHombus was non-geographical and too esoteric. RHinovirus perhaps.
"RH" is surprising - you'd want words that people would spell correctly, and PI/RI/SI/PH/SH seem easier to work with if you're trying to get 74.