My 2 biggest card sending times are Christmas/Hanukkah and Easter/Passover. I send cards to family, friends and students. I worked on the latter variety for a couple nights and have them written, addressed, stamped and sealed....early, for a change.
I used one of the cross seals I have for the Easter cards.
I used a Magen David seal for the Passover cards.
But, what to do about the family in whose single envelope will be both an Easter and Passover card? Go generic, with my You've Got Mail seal.
Because I was making a large number of seals, I used my low temp glue gun and the genuine wax sticks that fit into it (not the colored glue that some people use for decorative scrap booking and other crafts). Silver wax sticks were already loaded so I sealed the Passover cards first. I hoped they would require all the silver wax so I could use a pretty pastel purple wax I have for the Easter cards. It didn't run out, so the light purple wax will be for upcoming spring birthday cards, for which I also use the glue gun. I write all the birthday cards for a given month, at the same time. It saves time and I'm more likely to get them posted at just the right time.