 One piece of info you're likely to find printed on the top of an IC is a date code, specifying when the IC was made. It's especially helpful when a manufacturer needs to identify a defective batch of chips. Date codes are most often listed in the YYWW format. The first two numbers being the last two digits of the calendar year, and the second two digits being the weak number. So this at Mega328 was produced in the 47th week of 2013, which was the week of November 17th. Of course to keep things interesting, some chip makers list the weak number before the year, so when in doubt, check the manufacturer's documentation for their particular method.