When it's the BP/Amoco logo. The Vienna-based philosophy/design group Monochrom asked people to draw, from memory, as many corporate logos as they could. The results are surprising:
http://www.monochrom.at/markenzeichnen/index-eng.htm
Open the link and click on a logo, otherwise nothing really happens. It's interesting how long some of our memories of logos are. Check out the old star-shield of Philips, or the abbreviated-marijuana-leaf that once was Adidas.