I've just checked and the backlog on SP missions is about six weeks. So you submitted more than about six weeks ago, somebody is looking at your mission in some way, shape or form, or possibly waiting to hear back from you.
If you submitted less than about six weeks ago then your mission is something the reviewers still have to look forward to.
Six weeks sounds like a lot but it's a short time compared to how long it takes to create a good mission. Also it's the best it's ever been since.... well probably ever.
The backlog is longer for MP because of the greater difficulties of reviewing same.
If you want to check whether your mission is under review follow General Barron's suggestion and see if there is anything in pending comments. If it's blank, the mission has not yet been taken under review.
And I concur, it would be nice to be able to see what was where. Trickier than it sounds to implement though, and then you have all the complications of what about missions where there is a fault and the author has been contacted but hasn't replied, etc., etc..