RedStar Earth dating conventions.

"PiCo" refers to dates before Roavic contact. (Pre-Contact...PiCo)
"PoCo" refers to dates after Roavic contact. (Post-Contact...PoCo)
Easy peasy! Now, while I don't really think that making contact with an extrasolar culture would spur a complete change in dating conventions (A change from the B.C./A.D. or B.C.E./C.E. convention for those keeping score at home), I think it's convenient for two reasons.
1. It makes datekeeping easy by creating a new context in which to view the events of my conworld's history
2. I don't have to mention the real-world date!