Using some of the tools at AncestryDNA, I've been marking the matches that I can identify in a couple of ways.
If I know the relationship, I am using the Note feature to add a note to the match that spells out the exact relationship. This has come in handy when I've had to try to remember exactly how a match ties into a family.
These notes are edited when I click into the matches, but will also display the first couple of lines when I am at the main screen looking at all of mom's matches.
Another feature I've been using is the ability to color-code groups of matches. Ancestry gives you a color palete and allows you to create groups of matches that you can use in any way you would like. I've chosen to create groups based on ancestral couples, so I can tell in an instant what branches of ancestors the match shares with mom.
I use these groups to indicate the MRCA (Most Recent Common Ancestor) of the match. For example, if the match shares, Charles Lambertson and Pearl Beals, then I group them in the Lambertson-Beals group, even though they might also fall into the more recent Lambertson-Gilliland group.
Using these features, I've been able to identify and catergorize several matches without having to reach out to them and ask them how we might be related - I'm able to figure out our common connections and can decide who to reach out to for more information at a later date.