They are concave on the back. I didn't have a picture of them it the back. Thanks for asking, I will put that in the description next time I list this kind of charm.
This Silver is from Tibet and is likely 99.5% Silver, Tibet and China do not mark (hallmark) their silver. The 925 hallmark for sterlaing silver now most widely accepted is a result of a 1972 standardization of world hallmarking by the EFTA (European Fair Trade Association). Many non-European jewelers have adopted this system without the formality of a government mandated standard.
Here is a little lesson about silver. In its purest form this lustrous metal, like gold, is very soft. For this reason Silver is usually alloyed with other metals such as copper, as is the case in sterling silver jewelry, to make it more robust.
• Fine Silver [sometimes called Jerusalem Silver], is 99.9% Silver. • Thai Karen Hill-Tribe Silver [Tibetan Silver] is 99.5% Silver. • Britannia Silver is 95.84% Silver with up to 4.16% copper. • Mexican Silver is usually 95% Silver and 5% Copper. • Sterling Silver Jewelry is 92.5% Silver, with copper making up the remaining 7.5%. • German Silver [Alpaca Silver, new silver, nickel silver] isn't silver at all but an alloy of various metals with a grayish-silver colour. Pure silver is rather unstable and oxides rather quickly [this is one reason the silver plated items wear through the silver so quickly as compared to gold plated items since the gold is much less interactive and does not oxidize as easily]. Silver is sometimes intentionally oxidized or "antiqued" to highlight intricate designs as in Tibetan and Celtic designs.