RILM abstract: The English virginalists from 1530 to 1650 used signs in the form of an oblique stroke through the note stem to indicate a grace. The single stroke does not appear to have been used as a grace sign until around 1570 and was used frequently only after the later 17th c. The double stroke appears often; 16th-c. English keyboard music sources imply that it was realized with a form of shake. The triple stroke was used only in a small number of sources including 16th- and 17th-c. MSS. The sometimes idiosyncratic usage of signs suggests that composers and copyists may have used the signs with different intents."
"The Application of (Ornamental) Strokes in English Virginalist Music: a Brief Chronological Survey,"
Performance Practice Review:
1, Article 6.
Available at: https://scholarship.claremont.edu/ppr/vol9/iss1/6