By way of follow-up, I've wrestled long and hard about what to do regarding my Instagram account. On the one hand, I didn't want to leave all my photos there to be sold off by IG to a third party (as their Terms of Service allows). But with nearly 500 followers built up over the course of nearly 3 years, I loathed the idea of cutting myself off from a community of wonderful, creative people.
Last night I announced my intentions to delete my account. By morning, however, I began to question that decision. In the end, I decided to do the thing I didn't really want to do: start using watermarks for new posts. I also spent several hours purging old content, from my original 1,200 photos down to a modest 265. Culling old work was actually a refreshing thing, and reminded me of how far I've come as a photographer.
Most of the photos I kept were people photos. Knowing that any legit commercial agency is going to require model releases, I feel safe leaving those alone. Future posts, regardless of content, will bear a watermark. I'm still working on a standard look for that purpose; it needs to be a nuisance to remove but not so obtrusive as to ruin the viewing experience. That's always a fine line.
For those interested, I've found a useful app that will add customizable watermarks in the form of text or images. It's called Add Watermark Free. There's also a paid version which I may eventually buy once I determine a standardized workflow.