wrt serial nr. placement -

as stated by T-Mar, numerous manufacturers employed this placement. here are three examples. blue and white cycles are Vista brand. red bike is an Araya.







wrt head emblem -

Centurion had three sizes of head emblem at this era. They were used depending on frame size - head tube length. The brown cycle posted by MauriceMoss is a 23" nominal so it wears the medium size head emblem.