I'm not familiar with a certification sticker. does this mean they were certified to have been used for alcohol storage? Just curious.
I would depressure the kegs through the gas tap, take the bail out. Remove the in and out posts and the tubes will slide out. Because I am anal, I would break the posts down. Check all of the o rings and replace them as necessary. Some people change out all of the o rings. If they weren't cut and don't have a strong odor, I'd just clean them up. I would soak all of the broken down parts in the keg with Walmart brand Oxyclean overnight then rinse and dry them. When you break out the tubes, you can see if they have solids in them. Most of the time they don't but you can buy a brush to push through them if they do. I would get a brush anyway because now you will be addicted to kegging and you will need one eventually. Start looking on Craigslist, eBay, and ads on here for a CO2 bottle, regulator, and tap set up. There's no rush. If you filled them today, you're at least a month away from needing to tap them. Post any other questions. Luck - Dwain