I think something weird is going on. I was just at Michael's yesterday looking at the different mosses for a project. Not 24 hours later this shows up in my feed from Colin Weddings! Are you serious?!
Now clearly, this idea has been around and is not new. But it's not the type of idea that you see everyday. It's a stunning and clever way to get your tables marked without detracting from the elegance of the tablescape. The trick here, is to make it work as part of the design, rather than a clumsy after thought.
You can buy different kinds of mosses too! The craft stores carry all kinds. Faux and dried. Don't be afraid to buy these fresh from your market! LA has mood moss, which I love, down at the flower markets, but they also carry other varieties.
With a number template, some glue and moss, you can create just about anything you want that will be a cheap and easy way to DIY your wedding table numbers with moss.