If you take a quick look at the verses preceding this scripture you'll find that there was soon to be all sorts of turmoil going on. This is something we like to conveniently overlook when we are pulling out scriptures for ourselves. But God was assuring Zerubbabel that even in the midst of total chaos (which can be like many of our days!!) God still values him as much as His signature.
The king's signet ring was his seal on a matter. It finalized it and no one could argue with it or change what had been sealed. We are His signature on the earth and He will protect our souls even in the midst of trials, temptation and turmoil! Remember today how valuable you are to Him!