For reusable signs I have seen very creative ideas such as using pieces of slate or flat stone or painting smooth surfaces (like plexiglass) with chalkboard paint and then use chalk or chalk pens to write. See details on the blog post.
Another temporary sign that I have seen that seemed real easy was a pie shaped "slice" of a paper plate stapled to wooden post. It lasts about as long as the annual plant that it is labeling and can then be composted when faded, and new signs created.
Here are some Professionally Designed Garden Education Signs (both have a sign that mentions pollinators)
Here are some other threads on creating garden signage from our forum that might be of use to you as well: