Some of the cylinder manufacturers use a really thick paint that tends to obscure the original stamped markings on the collar. Sometimes holding it in various angles from the sun helps to reveal the stamped numbers/letters. And sometimes not, in which case I just use good sense: If the cylinder looks newish and is good shape, I fill it.
New cylinders are good for 12 years after initial certification at the factory in the USA. Canada's laws differ, I believe.
If the cylinder has already been recertified in the US, the markings are pretty easy to spot. Some recertifiers use stamped markings; others use a robust label. In any event, for a visually recertified cylinder, it'll have an "E" (think "eye") before or after the month/year date on which the recert took place. The cylinder is good for five years after that date. You can have it recertified indefinitely, as long as the cylinder is in good condition and no new laws prevent the recert.
Oh, final note. In the US, states -- not the federal government -- control propane handling, installation, filling, cylinder recert, and the like; laws governing these vary quite a bit from state to state, but most adhere at some level to the recommendations made by the NFPA
. (DOT and ASME set forth design characteristics for cylinder manufacture.)