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I think the most significant issue is whether anyone would know (or bother to find out) what "very positive" means in the context of some specific university's usage. Moreover, for academic purposes, very soon after your Ph.D. something like this becomes either trivial and distracting (because subsequent references to your dissertation and/or your publications in general will supersede anything this honor is likely to provide) or pretentious (if subsequent references to your dissertation and/or your publications in general are nonexistent or few). On the other hand, for non-academic purposes, it might be fine to do this.