Can reference characters be added to patent drawings without applicant’s annotated sheets?

Yes, according to MPEP 608.02(w), adding two or three reference characters or exponents is one of the changes that can be made to patent drawings without requiring annotated sheets from the applicant. The MPEP states:

As a guide to the examiner, the following corrections are illustrative of those that may be suggested without requiring annotated sheets from the applicant: (A) Adding two or three reference characters or exponents.

This allows for minor additions to improve the clarity of the drawings without necessitating a formal submission from the applicant.

To learn more:

• patent drawings
• reference characters
• drawing changes
• USPTO
• MPEP