What does “signage server: polling every 60 sec” mean?

This means that the player doesn’t have a direct connection to the server, maybe an intermittent connection or worse of all firewall issues that is often caused by either your networking hardware or internet provider.

We support both LIVE Sockets as well as HTTP Polling.
Under the SignageStudio  > Stations you may get 3 color indicators:

Yellow: connected via Polling
Green: connected via live socket
Red: not connected at all

To allow access to our servers be sure to open port 80 of both type: SOCKET and type: HTTP to the destination of: *.signage.me of inbound and outbound.
If you need explicit rules be sure to add:

master.signage.me = 198.65.158.173
business.signage.me = 198.65.158.174
neptune.signage.me = 198.64.149.167
galaxy.signage.me = 161.58.177.84
mercury.signage.me = 161.58.177.78
venus.signage.me = 161.58.177.82
mars.signage.me = 198.64.152.157

But note that servers are sometimes added so *.signage.me will allow fo greater flexibility.