Crest Location: As it so happens, this is the earliest of the available Crests - so early, in fact, it was even available in the original FFX PS2 demo, as I recall! On the beaches of Besaid where you first met Wakka, go southeast into the water. Along the eastern wall is an alcove in which you’ll find this.
Sigil Location : See the Remiem Temple (in full) section for proper details. Basically, after getting the Magus Sisters, speak with Belgemine in the Remiem Temple and opt to Send her.