The first side is the symbol of Venus from the Seal of the Seven Planets from Henrich Agrippa's second book "Of Occult Philosophy". It focuses on celestial magic and this is one of his kameas, or magical squares.
On this page -
http://www.esotericarchives.com/agrippa/agripp2b.htm you can see the symbols from the front and back (this is from the book listed above). The front is the full seal. The symbols on the back are for the Intelligence of Venus (the long M one), the Spirit of Venus (the backwards C with the circles on the end), and the Intelligences (the triangle weird one). The circle and plus sign symbol is the planetary symbol for Venus. Anael/Haniel is the archangel associated with this seal.
http://www.archangels-and-angels.com...gel_anael.html
So while I can say it's a magic square, can't say if it's associated to any groups in particular.
Here's some more info on Agrippa's magic squares -
https://en.wikipedia.org/wiki/Magic_...s_in_occultism
PS: Here's a new pendant from Etsy similar to the front -
https://www.etsy.com/ca/listing/671113578/seal-of-venus