Well, if you need a sigil for evocation, here’s Metatron’s and here’s Sandalphon’s.
I haven’t worked with either of them yet, I’m planing on making a grimoire of angels from the Abrahamic religions and so I’m currently data-mining looking for all sources of angels. But, just from intuition and my astral senses I can tell you that Metatron is a very high minded Ouranic spirit, the higher you are the better; and Sandalphon is very Cthonic, being very grounded on the earth. So, use that as a guide for effective communication if you want to work with them.