In group theory there is a global tag, group-theory. There are also a number of sub-tags, such as finite-groups, abelian-groups, topological-groups, geometric-group-theory, etc. I am sure there are similar sub-tags for other subjects.
Would it not be a good idea to put something on these tags to "persuade" question askers to also use the group-theory tag (or at least the abstract-algebra tag, although this is a bit general, but maybe that's just my opinion)? It seems a number of questions which are straight out of an introductory course do not tag group-theory, but virtually identical ones do.
EDIT: As suggested in the comments, I have done this to (most of*) the group-theory related tags. However, it would be nice if this was done uniformly across the board...
*I didn't touch the (group-cohomology) tag as it needs a tag in the first place and I do not really know enough about it to write one! It would be useful if someone more knowledgeable about this than me wrote it...