They trademarked a very specific icon which happens to contain the digits 2, 8, and 0 in that order. (If you have an iOS device, it is your "Maps" icon.)
They did not trademark "280".
A bit of history: when AMD and Cyrix started gaining market share selling their x86 chips, Intel went to court to try to trademark "486" and failed, so the 586 became Pentium.
There's a similar story that the Porsche 911 was originally going to be called 901, but that Peugeot had claimed all 3-digit numbers with a zero in the middle and forced Porsche to rename their model.
If the drug company that made the morning after birth control drug had not been able tom trademark RU-486, I wonder ifbtheymwould have called it Preventium?