If you are finding that Outlook 2016 freezes when you are trying to access signatures, the solution many times is to uninstall all the preinstalled Office applications from the computer.

When you install your own version of Office on a computer preloaded, when you look in the apps list you will see 2 Words, 2 Excels, 2 Outlooks etc. Uninstall all the preinstalled versions, and viola, signatures will work again. Simple fix and avoids reinstall.