Wha?

AP:

Speaking with reporters in Seville, Spain, on Friday before traveling to Munich, Gates told reporters that markings on explosives provide "pretty good" evidence that Iranians are supplying either weapons or technology for Iraqi extremists.
"I think there's some serial numbers, there may be some markings on some of the projectile fragments that we found" that point to Iran, he said.
Gates' remarks left unclear how the U.S. knows the serial numbers are traceable to Iran and whether such weapons would have been sent to Iraq by the Iranian government or by private arms dealers.

"Markings?" Do they stamp "Made in Iran" on them? Why would they do that? "Serial numbers?" Maybe they come with a warranty.