OK. So we can establish that this piece is 9 carat gold, which is the most hard wearing. Now for the tricky park, is it a diamond, aka "a girl's best friend" or a diamond fake like moissonite that can even pass for diamond on some of the lesser expensive diamond testers. This is where knowing the date of the article comes in handy. Moissonite only hit the market in 1998.
There are lots of "faux" possibilities besides moissonite diamond of course, but considering the article is gold, and it also sounds like it has a maker's mark, which are the letters "B & B" I would lean towards diamond - a girl's best friend type of diamond until proven otherwise.
If the diamonds are loose there is a simple way to test diamond but as this one under examination is set in the metal, you might like to take it to your local jeweler that you can trust and get it tested, if you can't stand the suspense of not knowing.