MiF2 with wing dot
This F2 with a dot differs from a genuine Mi2 or an F4 because the dot is connected to both the edge of the wing and the nearest "U" (representing a feather).
The dot on genuine stamps touches only the wing; the dot on F4's touches only the feather (or U).
Genuine Mi2 with fine perfs on top. Scan courtesy of J. Šimůnek. The original has a Janusz Berbeka certificate, translation courtesy of Roman Sobus.
This is a previously undocumented Mi2 type 6, "double line perforation error" (i.e. the perf wheel was run through twice without moving the stamps.)
Mi 2 Forgery Misperf Oddities
See other oddities: Cat #'s 2, 3, 4, 5, 6, 7, 8, 15, 16, 18.