INDEED… there are MANY sigil sites especially on Pinterest… You could choose one that is traditional or it could be really powerful if you make your own. I think @Linda6 suggested this, too and @Francisco has some references from the learning tools here on Spells8
SOMEONE PLEASE CORRECT ME,
Sigils are really very simple line drawings created with the intent to hold the meaning envisioned by the creator. (There are various tutorials to help create these)
If you are thinking about SEALS they can be quite complex.
I think Sigils and Seals are sometimes interchangeable but sigils are pretty universal and can be representative of a being or the intention of an action. A sigil could be representative of an entity and stand on the altar, or be used in spells to activate an intention or convey an action. It can be attached to an object for protection or activated by burning thus sending the intentions into the hands of the universe for fulfillment.
SEALS I have seen are usually representative of an entity (for protection or action by that entity) or representative of an action activated by a spell (healing, power, luck, good fortune, love, wealth) and then attached, carried or worn by the a person or object. Offering protection by the represented entity or as a tangible enforcement of the applied action - think talisman.