There are some pretty neat solutions to this. One of them involves a double layer ballot+receipt. When viewed on top of each other, they spell out the vote, but alone the receipt will just give you enough information to see if your vote is counted or not:
Another scheme is giving away fake receipts in addition to or instead of "I voted" stickers.
OK VLM your boss needs a Trump receipt, your communist college professor needs a Clinton receipt, you need another Clinton receipt for facebook and github or they will delete your accounts, that'll be one R, three D, would you like any complimentary green party receipts? OK here's all your receipts thanks for voting see ya in 4 years!
Heck hand them out with the bake sale goods. Have a free set of pre-printed fake receipts for ALL the candidates with some delicious chocolate chip cookies that fund this schools PTA. "Could I interest you in this cageless chicken egg gluten free organic soy oil brownie with a complimentary fake green party receipt?"
https://people.csail.mit.edu/rivest/voting/papers/Chaum-Secr...
Not sure it beats paper ballots and hand counting in terms of practicality, though :)