Anyway, here's my idea for this. Apologies if it seems crude, I only just thought of this.
If your journal is Friends Only, you may wish to place a banner in either your journal or User Bio to inform people of your journal's Friends Only status. You can place a banner into your journal in the same way you place images into your entries or User Bio. Please note that if you place a banner on your main journal page, it will need to be placed in an entry dated far into the future to allow it to remain visible to others. (EDIT: I read that the last sentence is correct, don't ask me where, I don't remember. If it isn't, please disregard the last sentence.)
Whew! that was harder than I thought!