CLP regulation: blank pictograms on preprinted labels
It is a common practice when preparing pre-printed stock labels to have four blank red diamond borders in order to print the necessary pictograms. Many products won’t use all the pictograms resulting in some being left blank. While the CLP does not explicitly forbid blank diamonds, any information in addition to the minimum mandatory labeling must not contradict or cast doubt on the mandatory label information.
Blank diamonds may cast doubt as to whether the product is fully classified and not simply missing a pictogram. In order to remedy this, it is advised you cover the unused squares with a solid overprint which blacks them out completely.
More information can be found in the ECHA Guidance on CLP Labelling and Packaging version 3 2017.