Ok so I figured out how it works #NotaTwitterUser but I don't see how it should be used for maximum benefit.
Related posts should be in a thread and if it used all over the place you'll get too many hits.
Depending on what is the intent to add this, hashtags can be beneficial or simply become screen pollution.
If Dave intends to get some statistics out of it, IME tags on a forum are very useful when there is a pre-set of them and not a "free-text form" - otherwise it can become a hodge-podge of random characters. I have seen things such as #helpmechooseanoscilloscopeplz or other very specific and impractical tags.
Obviously that creating such list can be impractical for such varied forum, although I could see at least some very useful candidates such as #TEA or #DS1054Z or #SDS1104X-E and so on.
If the intend is to help with cross-threading and related tags, I see the usefulness in, for example, the never-ending "entry level oscilloscope" threads, where someone can quickly find multiple threads related to the same subject - again, if the hashtags are somewhat "standardized" and meaningful. In this case, hashtags such as #chooseoscilloscope or #beginnerdmm could help with this.
I just hope the screen pollution is kept to a minimum.