I like th 'hum' symbol. A lotus to represent a new beginning, or a hard time in life that has been overcome and the symbol "Hum" from the Buddhist mantra to stand for love, kindness and protection.this symbol is also said to purify hatred and anger.
or I would get something with Snoopy for my dad. Because when I was little, he would buy me Snoopy themed Valentines Day Cards, and I would buy him Snoopy themed Birthday cards. We have never bonded over too much But when we have, it was with Snoopy