Normaly the stamp and other markers applied by the firms working with them are enough, as a normal bottle is its own certificate.

Things handy to know and to look for on a bottle.

Datemark of last testing-some bottles have up to 4 datemarks up on them. Every 5 years a bottle needs retesting, max age of a CO2 cannister is 20 years.
With a very new bottle a Pi stamp.
A country related pressure testing mark is another stamp common.
A tarra and netto weight, sometimes a volume is stamped in.
Test pressure and work pressure.
Brandname, or ownername-there are some Maddox branded bottles around, as the firm that does the CO2 bottles for me marks them as being mine.