Sync mark

 

Frame mark on lace-up leader of image and sound negatives to enable printing to be ‘in sync’. Also zero point for FCC counts.

 

https://www.nfsa.gov.au/sites/default/files/uploads/2010/08/31/sync.gif

References

Case, D., 1985, Motion Picture Film Processing, Media Manuals, Focal Press, London, Boston