I assume this team of two is going from project to project and establishing DevOps stuff there (creating CI/CD pipelines, supporting the other devs creating Dockerfiles, or whatever technology you are using). In other words, type 3, 4, 5 or 6 as per http://web.devopstopologies.com/ .
In this case, a sign of shortage is simply too much workload for those two; too many projects requesting their services; too many tickets; overtime; stress, burnout. These factors should be reasons enough for a responsible leadership to add more capacity. I don't see a DevOps specific sign in this, it's just a function that is understaffed.
Another sign to change something is if you take a good hard look and if you notice that you are creating a "DevOps silo", in which all DevOps know-how is concentrated in those two guys/gals, and everybody else just leans back because those two are "doing DevOps". That is not the point of DevOps. If this is the case, think about the cultural aspect, and modify them to be more evangelists/teachers/coaches for the other teams.
In both cases, the deeper reason of why having DevOps in the first place is a good thing (the general Good Stuff) should be clear to the upper management. If you cannot bring that message across, then scale down the work which your team is doing, by shifting it onto the regular Devs/Ops (as should be the case, anyways).