Another (and less known) one of Calvin's alter identities in Calvin and Hobbes. Tracer Bullet is a Private Eye, and usually cartoon strips with Tracer Bullet in it show a lot more shadow than normal. Normally, Calvin narrates a lot also (think of how private eye movies normally open). Usually, the damsel in distress is his mother, who is trying to get Calvin to fess up about destorying a vase or cutting his own hair. Bill Watterson (creator and author of Calvin and Hobbes) own words on Tracer Bullet:

Tracer Bullet stories are extremely time-consuming to write, so I don't attempt them often. I'm not at all familiar with film noir or detective novels, so these are just spoofs on the clichés of the genre. Cartoonists don't use black much anymore (the eye, being lazy, is attracted to empty white space, especially when the panels are so small), and we miss some dramatic possibilities that way.

From: The Calvin and Hobbes Tenth Anniversary Book



Also, bullets (the kind shot from guns) which leave visible glowing trails behind them.