According to NEC/IEEE/ANSI/UL etc should there be an indicator on the SPD to indicate that its service life is over? Otherwise how can a consumer make sure that it is in order?

You can't if there is no indicator. It's that simple.

Unfortunately, this is not a one stop shop to obtain the standards published by NEC, UL, IEEE, ANSI, etc.

You will need to subscribe to each agency to research each standard and find what your looking for.

NEC will not apply to your question.

You may also need to consider NEMA and NIST.

I thought someone in this forum would give an answer clearing any doubts

Doubt? Odd comment.

I gave you the answer that NEC is not involved. I personally can attest to that.

The other agencys and standards are beyond the scope of this forum.

While what you ask is required certainly makes sense, I do not believe there is a person here that is involved with the design, manufacturing, distribution, or otherwise directly involved with surge protectors, that would have first hand knowledge to answer your question.

I and apparently other do not have the time or interest to research the other standards that you mention, or the ones I suggested, to find your specific answer, nor do we have the funds to purchase those standards.

I answered you as if you're an engineer in some discipline, and you should be the person to take the time and funds to research the question.

If you have a specific unit in mind, something you have and noticed it does not have an indicator light, and you think one would be a good idea, contact that manufacturer directly and discuss the subject with the design and marketing team. You should discover if there is a standard regulating this indicator light, and why one is not installed.

A person involved in manufacturing,marketing or installing SPDs should know the answer. We can't search all available standards/codes for a simple question.