Security depends on the Marina itself. Lock your boat yes but it there is little security at the marina it wouldn't matter. You can get into even expensive boats with little more than a screwdriver. Some boats have alarms.
Walking the docks to check out what others are doing is a good idea. I'm the only one on this dock that uses double lines. They are not needed if you live close enough to check the boat now and then. Same with sails, you can leave them on if you are close enough to remove them when a storm is on its way.
Part of the etiquette is to keep an eye out. Talk to people, if someone seems out of place talk to them to see if you can help. Stuff like that goes a long way to helping keep the place safe.
I do not like to touch other boats though I did find a big fender floating around and tracked down which boat it was from (that was fun) and then tied it back on.
When I notice problems, like a sinking boat or broken dockline, I report them to the office though I did snap back on .
Ask if someone needs help when coming in or going out. Most folks don't but it can be handy just to have someone on the dock to throw a line to and if you are walking by why not. Some marinas are so tight that having a hand on the dock is about the only way to get in or out.