sure looks like theres a spring. the upper right terminal where the arrow is.
I thought you were referring to a spring that touches the battery, but I see what you mean now. The arrow is pointing to the switch which may have a spring inside or magnets that do the work of a spring. I have one mod that has the switch between the positive end of the battery and the center post of the 510 connection. In that mod I place the battery positive end toward the switch.
What matters is that we don't allow a negative battery casing to make contact with the positive side of the circuit. Mod enclosures, if they are part of the electrical circuit are designed to be ground (negative side of the circuit). Reversing the battery in a mech mod will make the enclosure positive.