I jumped into game to see if I could figure out what's happening. I think I was able to get it to work. Here's the steps I took:
1. Get into game, go to Live Mode, press pause and make sure testingcheats are on [Press Ctrl-Shift-C together and type in testingcheats on]
2. Type or copy in the cheat: bb.showhiddenobjects true - hit Esc to get out of the cheat console.
** Note: bb.showhiddenobjects on, may give a failed message, so try bb.showhiddenobjects true instead. If it doesn't say failed, go to next step.
3. Enter Build/Buy mode and in the search bar type debug -- After that, all "hidden" objects should be available to use.
-- Search by Base Game. Fishing signs and ponds should be near the bottom of the list.
This is what debug showed when I typed in debug. Click thumbnail to see larger view.