I just got into reloading shotgun shells. I have a lyman 525gr slug and to mark the hulls I created and ordered a rubber stamp design. The Staz-On solvent based ink sticks and dries to the hulls just fine. I used metallic silver as it will show up on all hull colors. Yellow was my next choice but there are some yellow hulls out there. The stamp is on a is a .5x1" stamp pad.
I have a 12ga design and the skinnier longer 20ga design. The one pictured below is 20ga design on a 12ga hull. I liked it more.
PM me with an Email address and I'll send you the two files you can upload to:

Takes 1-2 days for them to ship.
Rubber Stamps

They're $4.95-5.95 per stamp and you just upload your design to them.

I used to reload a LOT of 12ga before the price of lead skyrocketed and my sources of free wheel weights evaporated.  I always used a Sharpie and it lasted a long time before it became illegible.  With the amount of trap shooting I do (~4k/month), it's simply not worth the time time do it anymore.  Cheaper to buy flats.  

I like the design, though.  Pretty cool for a touch of personalization.

I wouldn't mark trap loads, just the slugs. For buckshot I simply dot it with a silver sharpie for each 0.  I mark the tops too in case they are in a sleeve.

One last bump for the night crew.