Once again late, but instead of such obvious indicators that a weapon has spawned like the suggestion of steitzer announcing it or it showing up in the hud, why not just have the ordnance drop as it does now, but regularly?
It adds another layer to being a good player. What I mean is, if we're on Valhalla, we see the ordnance spawn incoming. So in addition to knowing the timers, in case it slips your mind, you see it hurling down from the sky. Would make you more aware. Now naturally, it shouldn't kill you if you are over the spawn point, but I can see some hilarious situations where someone is going on a flag capture run on a warthog and ordnance incoming just blows them sky high.
And for the ordnance inside caves or bases, make it have some sort of audio cue that only those within a 5 meter range or super close can hear it. Like a loud metal thunk that the ordnance door opened or something.
Just a suggestion, I know it sounds weird, but when I thought about it, it makes sense for weapons to be dropped down in war games as opposed to just magically appearing. If you don't like people can die from it, make it so it just pushes someone underneath it away slightly.
And if you need additional help, much like the Palmer introductory vid, you can have a page of all the maps in war games. You get an overhead view and where the weapons spawn. Much like how gears showed the maps during loading. Pro players and newbs can learn the maps and spawns before even playing a match. Naturally you want to keep some skill involved so weapon times won't be known, people will have to learn how often a spartan laser spawns.