What Does It Mean?

Monster, I've hung around a few antique shops in years past. These people are mercenaries and don't miss a thing. For ten bucks, I think it highly likely that the candle holders are silver PLATED. The underlaying metal is possibly pot metal or, at best (and unlikeliest) brass. No antique dealer is gonna put out a solid silver item and sell it for less than melt value; most likely, s/he's gonna list something such at that for three to ten times melt.

Weight is one way of telling. Also on old silver it will be hallmarked (makers name, date, etc..) and on newer pieces it should be impressed on the underside with the makers name and the world "Sterling"
Ron

Sterling silver will be marked Sterling or 925, tableware of the early 1800's was made from 75% silver and will should be hallmarked, than there is Britannia silver which is 95.84% and maybe marked 958. Old Mexican silver is 95% silver and German silver is 80% silver.
Coin silver is 90% and Fine silvert is 99.9%

I have to admit that I don't know what the 620 means, but the weighted candle sticks are made from thin stamped sheets of sterling silver and they are filled with a sand/morter type mix. The silver sheets are very thin, kind of like the thickness of the metal that aluminum cans is made from. A two pound candlestick will probably contain less than an oz of silver.