"What symbol(s) do Christians use?"

Christians have a few symbols considered to be important but the most prevalent and recognizable one is the cross. The cross represents the sacrifice made by Jesus, Son of God.

"What symbol(s) do Sikhs use?"

Sikhs have quite a few symbols that are used but most of these symbols are physical items. These items include; Kesh (uncut hair), Kanga (special comb for their hair), Kara (metal bracelet), Kachera (undergarment) and Kirpan (small curved sword).