[perezdev]

It's the null propagation operator.

[breischl]

Look, if you want to be pedantic it's the null conditional operator[1]. But it is widely called the "Elvis operator"[2].

[1] - https://msdn.microsoft.com/en-us/library/dn986595.aspx

[2] - https://www.google.com/#q=c%23+elvis+operator