On land, I think I'd have to build lots of well marked roads with cleared shoulders. Also would burn some food early to get charcoal for signs. Probably leave North pointers every so often when I was sure of the direction. A single cheap pole fence with a sign would probably work for leaving known directions to stuff.

On water.. eesh.. best I can think of would be to make raised earth pillars with sheltered campfire atop using roof as reflector. Still limited use as range would be short. Would try to limit boat trips to destinations I could see from shore or near shore landmark/lighthouse.

Although.. this might not work but... ships don't move if a player isn't aboard. Could use rafts as breadcrumb trail?

Will be interesting to hear how you all do, and what solutions you find. You're braver men than I :)