As with any other event, DC promoted ARMAGEDDON 2001 in its comics during the run up to the event.
Main Series and Annuals
The main ad for the series promising changes for multiple characters 
An ad with a checklist of titles 
An ad specifically for the JUSTICE LEAGUE AMERICA annual 
And another for the ACTION COMICS annual 
An ad for FLASH and HAWKWORLD annuals 
An ad for SUPERMAN and BATMAN annuals 
An ad for the NEW TITANS and LEGION annuals.
ARMAGEDDON: THE ALIEN AGENDA
Despite the story being about Captain Atom trying to stop Monarch, the ads clearly focus on the bad guy!
Crisis on Earth-Prime 