We have a little 'Coffee Cartel' in the office. This is a group of individuals, selected primarily through unapologetic nepotism, who contribute to a supply of ground coffee and partake of the same twice-daily cafetière. We're not all from the same team, and as members have come and gone or moved around the building the method of notification when the brew is brewed is important.
Over the couple of years that this little scheme has been running internal email has been the most reliable method. When an email arrives with no subject and no content other than a (generally silly) picture then all parties know that the coffee is ready. The truly interesting point, at least from my perspective, is that these e-mails are in greater demand now than the coffee. Colleagues uninvolved with the cartel have requested to be part of the mailing list alone, just to receive the pictures, which have become a bit of a talking point around 9:30 and 14:30 around the office. These little things truly do take on their own meaning, becoming more than they were intended to be. While the amusement is limited, it's clearly become of passing interest to far more people than anyone could have anticipated.