I could imagine that in the USA it's different - in fact, do airlines in any other countries try to have significant registrations
There's less scope in the US, obviously, as all registrations are at least partly numeric with a maximum of two letters optionally tagged on to the end.
Where airlines are concerned, the best they can usually manage is to have their IATA designator (AA, DL, JB, etc) as part of the reg.
Some GA aircraft have pseudo-personalised marks, for example Occidental Oil (Oxy) have managed it in the past:
