Weird symbols for key combinations on a Mac

Here's a chart from OS X Keyboard Shortcuts that lists all the main icons, their primary names, and alternate names/symbols:

This Apple fansite has a similar list on a page with other Mac hints.

OS X Keyboard Shortcuts also provides descriptions for the most commonly seen icons. This official Apple site is similar, but is targeted at new users making the switch from Windows.

And as a bit of historical trivia, this Folklore.org blog post explains where the Command icon came from. The original idea was to use the Apple logo, but Steve Jobs decided there were "too many Apples on the screen!" and ordered a change. The icon you call "weird" and "like a clover" actually started life as the campground symbol on Swedish road signs.

I remember seeing some of these icons drawn on the keyboards of older Apple computers; why they were discontinued, I don't know.

_{(An earlier revision of this answer contained links to Apple documentation that stopped working.)}