Last night I went through the exercise of trying to find serial numbers on all my gear. This was not an easy task as the location of serial numbers varies from item to item. The serial numbers for the camera bodies were easy to find and in the same place for all three - at the base near the tripod screw. The serial number for the 580EX II Speedlite flash was also easy to find.
On the lenses it wasn't so easy to find serial numbers. In my search on the Internet to find information on serial number locations, I came across Ken Rockwell's site. Ken has very detailed reviews of Canon lenses and includes the location of the serial number in the review. A couple - the Canon 24-105mm f/4L IS and the Canon 85mm f/1.2L II USM - had serial numbers on the mating flange of the lens mount, and others like the Canon 70-300mm IS USM and the Canon 28mm f/1.8 had the serial number burnt into the black plastic. Note that older lenses have a date code (for example, my Canon 200mm f/2.8L II USM) which is not the serial number.
Not all of the equipment had serial numbers. For example, the battery grip for the 30D (BG-E2N) has a serial number while the battery grip for the 5D (BG-E4) appears not to have one. I also don't think my ST-E2 Speedlite Transmitter has a serial number.
The plus side of this exercise was that I was able to clean up and neatly organize all my gear. I love storage containers - it makes finding items very easy while keeping my workspace free of clutter (and safe from my curious cat).
