Phone is SM-G900V and am using in USA, specifically California. Android version 6.0.1 I did just notice that the signal is very weak, unlike my former LG3 phone which always had two bars at least. Our Samsungs usually have only one bar at the most.
Thanks for any thoughts.
The G900V carrier branded model of phone for the CDMA network, Verizon, will be reasonably compatible, (Band13-700MHz, Band4-AWS), with that network on 4G/LTE but may not be fully compatible or not compatible at all with certain other U.S. networks. See, Will My Phone Work.
Also, there is no industry standard for signal bars, so it is meaningless to compare them.
You could install Network Cell Info Lite, free from the Play Store, on your S5's and LG to get an accurate readout of -dBm and ASU strength. The lower the -dBm and the higher the ASU, the better.
That's not a lot to go on: could be anything from your account running out of credit to a glitch in your provider's systems, your SIM having failed, you've fiddled with the "testing" menu and changed your radio interface settings, your phone's transceiver has broken, someone is using a cellphone jammer nearby, there's a civil emergency and civilian phone services have been disconnected(*),...
We'll need more information if anyone is to be able to help you.
(*) That may sound facetious, but it's happened to me twice, on opposite sides of the planet. That's twice more than I've run out of credit, so if I base this only on my personal experience it's one of the things I'd check first . Seriously though, we know nothing you don't tell us, and those 4 words allow a very wide range of possibilities.