It is difficult without any tools. Here is a non-leader prospective.
I do not care for the current Meta so do not battle. My trophy count would not change if viewed. I do however play many hours a day and collect only.
I do not make requests for DNA. A big part of the game for me is to find and dart what I need. I do max a lot of requests as I dart all day so have excess of DNA for many desirable critters. But, unless someone requests what I have in abunance, they would not see a donation from me. I do not donate incubator only DNA as I do not get any of it anymore.
I will occasionally remark in the chat, but it is so buggy for me to even have a response appear that I do not use the chat. I will look at the donation requests but not read comments there as I usually cannot respond.
Anyone looking at the alliance would see my trophies not changing and see no requests from me, so think I am not active.
When Alliance missions were completed I received Top Contributor for 3 – end Rank Collector catagories as well as several lower ones along the way, but none in Defence. That is the only way a Leader would even know I am active. I do complete the daily battle incubator, but only for consideration of the alliance and only for the count. This week I am not battling, at all, as there are no missions. My name would never appear as a top contributor in any Defence category. I could see someone not quite as active as myself playing a lot and missing any mention in the Alliance missions.
If it were not for my IGN appearing in the Collector missions, I would be seen as inactive and booted from many Alliances.