How can I tag an instrument which is not in use as per ISO norms?

If you have some instruments that are not in use and are not calibrated, you should make sure they are kept in a place properly marked, and the instruments have the proper tag on them so they are not used. In addition all work places can list the measuring instruments not in use.  

The following material will provide you more information:

- Monitoring and Measurement Equipment Control - https://advisera.com/9001academy/blog/2014/05/06/monitoring-measurement-equipment-control/
- Free online training ISO 9001:2015 Foundations Course – https://advisera.com/training/iso-9001-foundations-course/
- Book - ISO internal audit: A plain English guide: https://advisera.com/books/iso-internal-audit-plain-english-guide/

We assigned an ID for those documents to keep the track where they are, who is responsible for handling, etc., we identified those equipments with the ID and also a red legend of "Just reference";  in our procedure we specified that those type of equipments, can not be used on production floor or in any process where the quality of product or process will be confirmed. 

We also audit those equipment, to confirm the proper storage and area. No issues during external audits with this process.