If you are a mod of a subreddit instead of going dark set it to restricted and have the welcome page link to the kbin/lemmy version of it.
Reddit Migration@kbin.social – 58 points – It will also help if you can set as many threads to nsfw as possible.
This will work until links to alternatives are banned anyway. Twitter tried it and were forced to roll that decision back, but I'm not sure if Reddit would have to.
Subreddit mods aren't going to push people toward Lemmy unless they're also on lemmy and have a community space already set up.
People who have invested thousands of hours into a forum don't generally want to merely direct people away. They want to migrate as much of it as possible to a new space, while maintaining the structures that manage things.
So, moderators need to a) decide Reddit is over (remember, the protests are trying to maintain the status quo and "save" Reddit, not to get people to leave), b) set up a space for community members to migrate to, and then initiate migration as best they can. Anyone invested in maintaining Reddit isn't going do that.