Dealing with this issue in my own layout design, I have concerns about putting something so sticky-outy on a relatively immovable foundation. Wayward hands tending to normal layout issues ranging from scenery tweaks to track cleaning to handling derailments have a tendency to find fragile bits such as signs, trees and signals. A highly-detailed signal mast with no give to it is a candidate for heads getting crushed or ladders being broken, at minimum. I have a bunch of BLMA signal bridges to spread around; these are super-delicate, needing to be given every opportunity to survive those wayward hands I mentioned.
The particular solution I'm working on is to put a connector up top as part of the signal base, using 0.050"-pitch 2X header connectors. David's approach with the barrel foundation is good, even great, and I'm going to steal the idea 
, but the barrel (possibly with a flange) will hold a receiving connector. With the male part of the connection on the foundation and the female connector hidden in the signal base, there should be plenty of give if the mast or bridge is nudged.
What happens underneath in terms of the decoder or other logic can still be part of the foundation. My personal preference happens to be electronics on a separate mounting plate, but whether the connection is direct or via a ribbon cable in that case is irrelevant.
Plugging and unplugging signals (NOT necessarily disconnecting the magnet wire) to allow for cleaning track seems like a really, really good idea.
-Dave
I understand the want... the issue that I'm having is that in order to place a header on the bottom of the current base (the high-res concrete 3D printed one) it would have to be a 1 mm pitch SMD 5x2 header with guide posts, like this:
https://www.digikey.com/product-detail/en/sullins-connector-solutions/SMH101-LPSE-D05-SP-BK/S9220-ND/2039524... and even then you'd have issues with the signal not coming out of the hole very well.
I don't want to leave you guys without a solution though, so maybe I can propose one. If you leave extra wire in the tube that connects the top piece to the the bottom piece of the signal base, you would be able to gently pull the signal out of the base and lay it on its side on the layout. If you're doing track work, just pull the signals out and lay them on their side. Or you could paint the poles orange and put warning lights on top of the masts for "airplanes"
EDIT: after reading railnerd's post again, it looks like I'm not the first to suggest this.
