You may notice some thumbs up/down icons on the server browser now. These only show for modded servers and they indicate whether or not a server is running mods that are verified (thumbs up = verified, thumbs down = not verified).
What does it mean for a mod to be verified? It means that a mod is confirmed to have come directly from the developer that it claims to have been written by, without having been tampered with. If every mod currently active on a server is verified and the server has mod verification turned on, then the server will get a thumbs up icon in the browser.
So how do you turn on mod verification? With the sv_mods_verified - set it to 1. Note that it is 0/off by default and will be turned off if any of your active mods fail
How does a mod get verified? It needs to first be registered - currently the simplest way to do this is with this app, and then it needs to have a registration.json file generated and distributed with it. Mod devs should therefore generate a new registration file every time they make a new release. This can be done with the same app used to register the mod in the first place, or alternatively a script like this can be used to do it over the command line.
This might seem a little tedius at first, but once you've done it once its really quite straightforward. Additionally, this is only the first phase in a move towards a more managed system of mod distribution. For example, it'll soon be possible to setup your servers to auto-update their active mods whenever a new release of them is made.
I think I've covered the broad strokes of the system, but let me know in the forums if you have any questions.