On my previous community we had the policy to carry this disclaimer in our signature: I am an [company name] representative but the views shared here are my own.
However I haven't seen this in almost any of the many communities I have visited in the last few years any more. I personally think that the signature field can hold more meaningful (or at least fun) content than that, such disclaimers should better be found in the terms & conditions, a guideline or somewhere else.
When it comes to sharing your own views, I actually think that this contributes a lot to a positive user / brand experience on your community. Of course there should be boundaries (my former Manager @Ditte always used to say "Don’t say anything your CEO wouldn't say” as a general hand rule), but representing an own opinion helps to "show the face” behind the (usually rather unpersonal) brand.
I feel that users really appreciated that they have someone responding in a different way than the rather canned, standard responses that they would receive from e.g. email support. I believe that this helps you also build up somewhat of a credibility. All of this together makes re-visits and further engagement much more attractive, as they feel they get a genuine response back rather than transactional handling of their ticket. Until this day I am convinced that this formed a substantial contribution to the success of that community.
Needless to say, this requires a good feeling for what can and should be said. Enjoying such a freedom also comes with the responsibility of knowing the impact of your response. I would for example never be publicly criticise my own companies decisions or post anything which is completely contrary to what the brand stands for.
Here a practical tip which probably will help you more than a signature: When you start sharing your own opinion, always communicate this to your users. When you check my responses, you will find a lot of "In my opinion...” or "I personally find that...”. I have internalized to always start my sentences like this when I am speculating or sharing my own, unapproved opinion. This ensures the customer understands that you are sharing your own view, but also shields of your company from any unwanted misrepresentation of values.