I like to use a dynamic banner with alternating message: one for visitors, one for new members (displayed after they signed up and until they reach the next trust level).
You could try this component: Manuel Kostka / Discourse / Components / New User Banner · GitLab. You can set the max trust level for new users (until which trust level the banner is shown) as well as outlet location and route:
The messages are html blocks and you’d also need to add custom styles. It’s a bit technical probably, but it can work nice when adjusted. E.g. here’s an example from a community:
