Based on what I read on the DNR site, you only needed to pay the excise tax and pay a $10.00 fee for a documentation sticker. It looks like the Documented vessel sticker is good for 2 years.
But I'm not from Maryland, there are plenty of Maryland sailors here, who must own documented vessels and can weigh in.
Here's the relevant links:
Maryland Department of Natural Resources - Boating
And the form : http://www.dnr.state.md.us/download/DNRB-240.pdf
There's a box at the top for Decal only..for Documented Vessels
But you appear to know this.
At $5.00 per year, I would just pay it, and save yourself the aggravation.
It also looks like you can mail it in...
I'm a documented vessel and have to pay $52.00 per year to register my boat in NJ. The only thing Documentation affords me in NJ is not having to put the numbers on my bow.