Shown in two styles, Davison Impacta (shown) and Davison Impacta Shaded (open with solid SE shadow) [PLINC One Liner 1971]. At least the latter is also shown in their 1969 Alphabet Yearbook. Already used in 1967.
Photo(s) by Groove is in the Art on Flickr.
Contributed by Florian Hardwig
Contributed by Matthijs Sluiter