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