Well first you are confusing 2 things. Coalition troops spawn with forest defenders. Stronghold troops are donated from your alliance. i doubt stronghold will turn a light on when full like bunkers since we are talking money, event, and expedition troops. Yes i know that that feature isn't working now. Trust me everyone is complaining and writing c.s. i would assume a fix is imminent.
so to tell the coalition, scout the base and look at embassy, of course this requires you to have memorized all the previous flags that no longer show anywhere else. All though not perfect it's best we have until they fix it. I hope you can check wiki to compare flags i have not looked yet, as we are not facing a challenge this war. You can also send one of your low armies to the base first and that way you can see the level and the coalition that base has from the report tab.
So devs please fix this soon as all the workarounds are difficult, time consuming, and wasteful