Slogan of many a German (5)
I believe the answer is:
motto
'slogan' is the definition.
('motto' can be a synonym of 'slogan')
'many a german' is the wordplay.
'many' becomes 'm' (**).
'a german' becomes 'otto' (I've seen this before).
'm'+'otto'='MOTTO'
'of' is the link.
(Other definitions for motto that I've seen before include "Phrase in a Christmas cracker" , "Phrase to express character" , "Guiding adage" , "It may be proverbial" , "(Family) maxim" .)