The methods we use to signal in-group membership often involve the use of group-specific jargon that will be unfamiliar to outsiders. This helps us mark who "gets it" as in-group members and who does not as members of the out-group. I believe that this is one of the functions of Christianspeak. Some Christians, especially evangelical fundamentalist Christians, use this as a way of signaling that they belong to the group and connecting with others who do so. This sort of signaling often distances them from out-group members, but they seem to be okay with that. After all, those outside their evangelical fundamentalist Christian group are likely to be bad people.
This sort of in-group signaling is hardly specific to Christians or other religious persons. I expect that we have all encountered secular examples both online and offline. Consider the social justice warriors and the jargon many of them use (e.g., "safe spaces," microaggressions, "mansplaining," intersectionality, triggers, "lived experience"). Like the evangelical fundamentalist Christians, such signals identify in-group members and separate them from the out-group. And like the evangelical fundamentalist Christians, this is preferable because the out-group is assumed to be rife with bad people (i.e., misogynistic rape apologizing neckbearded MRA dudebros who are "part of the problem" for being reluctant to "listen and believe").
What about atheists in general? Do we see this sort of in-group signaling among most atheists? Yes and no. We can easily find examples of atheists doing in-group signaling online in the form of sharing the same memes over and over on social media. At least for those living in the U.S., the frequency of this sort of behavior seems to spike around various Christian holidays. And I would bet that lots of in-group signaling takes place at large gatherings of atheists (e.g., conferences).
But what about the rest of the time? I think we see a difference here between groups like evangelical fundamentalist Christians or social justice warriors and most atheists. While the evangelical fundamentalist Christians seem to throw up their signals almost everywhere and many social justice warriors do the same with perhaps a bit more discretion, there are relatively few situations where one would expect to see atheists doing so offline. I suspect concerns over safety and religious privilege might have something to do with this difference.
For many atheists living in many parts of the U.S., indiscriminately signaling one's atheism to an unfamiliar audience is a risky endeavor. The prevalence of atheism in such an audience is likely to be very low, and hostility against atheists is likely to be high. Online signaling is far less risky, and signaling in environments where one can be assured that there is an artificially high concentration of atheists is even less so.
To some degree, what I have just said applies to social justice warriors too. You are probably more used to encountering their signaling online than you are offline. I see a fair amount of it offline in university settings, but I do not regularly encounter it in many other offline environments. I'd bet that those of you living in politically progressive areas and/or involved in lots of progressive activist groups offline run into it more often than I do.
Given their numbers and privileged status in U.S. society, Christians rarely have to worry about negative consequences related to in-group signaling. They can go so far as to adorn their vehicles and their persons with pro-Christian sayings and imagery. Here in Mississippi, this is so prevalent that it helps to define the experience of what it means to live here. At least once a week, I encounter a Christian who has never met me and yet feels perfectly safe in telling me all about his or her Christian faith regardless of how inappropriate it may be to do so given the context that brought us together.
I do not think there is necessarily anything wrong with signaling in-group membership. The pull to do so seems almost universal, and being able to sort people into in-group and out-group categories may have some advantages. It can become problematic when we take the additional step of demonizing the out-group on the basis of their out-group status (rather than their behavior). This is where I'd hope to see most atheists make fewer mistakes than evangelical fundamentalist Christians and social justice warriors even as I recognize that this is not a terribly realistic hope.
