Cargo depots have their restricted ocean access telegraphed on the water. When deleting the cargo depot the telegraph stays behind (is not deleted with the cargo depot as expected).
Before restarting the game:

After restarting the game:

save_22-07-26_23-39-39 cargo depot telegraph test.save
When testing with a new cargo depot it's the same when building it. The telegraph isn't enabled when building, so have to restart the game to see it.
COI 0.4.8
Files not imported: save_22-07-26_23-39-39 cargo depot telegraph test.save