Plus

It starts here. One plus one. Me plus you. Coffee plus donut.

There is nothing hidden in a + sign. It stands with its arms open, welcoming more numbers into the fold. It is the most optimistic of all symbols.

Compare this to Sigma ∑. Sigma is just "Plus" trying to look smart in a tuxedo, shouting at you to add up an infinite series. Plus is your friend who just wants to give you another slice of pizza.