Advertising - Since it's difficult to infer tone in an email, you should assume all mine are sarcastic or bitchy.

Here's your new email signature.

With human resources constantly going on about their silly rules concerning "etiquette" and "proper workplace discourse" and "not making overt threats of violence to your cubicle-mate," it can be hard to let your coworkers know just how big a part they play in your daily misery. These cards can help you get your point across as passive-aggressively as possible. You can just print them out and hang them in your cube to send a general message to anyone with eyes. Or, click on any card to share on the Facebook and Twitter accounts you know your coworkers follow. You can even send them to your targeted coworker from an anonymous someecards account. They'll know, but they'll never really know.