Unknown notation relating to stoichiometry
It is probably supposed to be the 'corresponds to' sign[ref, p 105]; in this case simply representing that for every two moles of $\ce{NaOH}$ one mole of $\ce{H2SO4}$ is converted by reaction stoichiometry. 

This sign is difficult to typeset in LaTeX which is why I presume the authors used something else instead. Creating the sign is even more annoying in MathJax. The closest I [got at first] were 

$$\overset{\lower.5em\wedge}{=}\ \text{or}\ \hat{=}$$

which are $\overset{\lower.5em\wedge}{=}$ and $\hat{=}$, respectively.

Edit. After some testing, this option $\lower.1em\lower.5em\widehat{\raise.5em{=}}$ looks best in my opinion.

$$\ce{2 mol NaOH $\lower.1em\lower.5em\widehat{\raise.5em{=}}$ 1 mol H2SO4}$$

full code: $$\ce{2 mol NaOH $\lower.1em\lower.5em\widehat{\raise.5em{=}}$ 1 mol H2SO4}$$

Just the bare $\widehat{=}$ leads to

$$\ce{2 mol NaOH \widehat{=} 1 mol H2SO4}.$$



ref: E. R. Cohen, T. Cvitas, J. G. Frey, B. Holmström, K. Kuchitsu, 
R. Marquardt, I. Mills, F. Pavese, M. Quack, J. Stohner, H. L. Strauss, M. Takami, A. J. Thor. (2007). Quantities, Units, and Symbols in Physical Chemistry. ('IUPAC Green Book'). Third Edition. International Union of Pure and Applied Chemistry. (2008 IUPAC &amp; RSC reprint). ISBN: 978-0-85404-433-7. [free copy] 

Here is a picture of how it looks in the 'Green Book':