I did not think that a +P specification for 40S&W was ever approved by SAAMI? But some ammunition manufactures puts +P on there 40 S&W. From the head stamp and a quick search of the internet I think the ammunition was originally from Intrac Arms International MFS.
The listing over at Cheaper than Dirt [http://www.cheaperthandirt.com/ctd/product.asp?sku=AMM-543] has the following description.
Law Enforcement Grade Ammo Ammunition designed for maximum penetration and stopping power, while still bargain priced; all +P ammunition for top performance, brass case, boxer primed, non-corrosive, ISO 9001 standard quality, within SAAMI and CIP standards. .40-S&W, 170gr, FMJ+P, 1200FPS and 542ft lbs.
I found the case last night in my box of range brass as I was reloading from. I sort though my brass and only reload Federal, Remington, and Winchester brass the rest gets dropped in a bastard brass box. Have any of you guys encountered +P 40S&W?