The symbol 
most commonly used to denote the adjoint operator. The
dagger is also known as the obelisk, obelus, or long cross (Bringhurst 1997, p. 275).
Dagger
See also
Adjoint, Double DaggerExplore with Wolfram|Alpha
References
Bringhurst, R. The Elements of Typographic Style, 2nd ed. Point Roberts, WA: Hartley and Marks, 1997.Referenced on Wolfram|Alpha
DaggerCite this as:
Weisstein, Eric W. "Dagger." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/Dagger.html