Can Teleportation signs be used in the Frontier? I ask because being 5,000 blocks away from an Outpost to be "Established" makes it a long run even a long electra flight to get back to town. Thank you
No, sorry, it's part of the vanilla approach of the server. Players use nether transport, boats, elytra, rail to get to and from outposts, some are thousands and thousands of blocks out. You could choose to have your outpost on one of the SMPs where you don't mind not being in town, you can still TP around town in the other 9 SMPs, but you can't transport items back and forth without travelling.
In my opinion, 5,000 blocks isn't crazy far, and with elytra flight, it's quite quick. However, if it's still annoying, I recommend finding a close stronghold somewhere in the wastes. As long as your respawn point is set at your frontier outpost, you can usually set up a quick warp from the end to your bed. This is what I do and it works well for me. But teleporting signs in the frontier would be antithetical to the experience that is supposed to be attained in the wild.