Just like writing direct and inverse limits in TeX, the way to write Čech cohomology groups in TeX is something that doesn't come up easily in Google unless you know what to look for (basically a list of math mode accents, but I am not the only person obstinately searching with the wrong keywords, right?).

So in text mode you write \v{C}ech, and in case you wish to write down the $n$-th Čech cohomology group $\check{\mathrm{H}}^n(X,\mathcal{F})$ of a topological space $X$ and the sheaf $\mathcal{F}$ you use \check{\mathrm{H}}^n(X,\mathcal{F}). Notice the use of \mathrm{H} for the actual (co)homology object, you could/should do this too!

Don't shoot the nitpicky typesetting aficionado please. And consider using a macro like \newcommand\HH{\mathrm{H}} for easier typing. And of course \newcommand\cHH{\check{\mathrm{H}}}.

Let this fact be known too.