What do these signs mean in some digital timing diagrams?
~ means a space in time , not to scale , in architectural or Mech dwg they might do that too 

    but not a time in space... but yet saves some.



It saves space to truncate a timing diagram.
It means between the wiggles. there is no time scale, it's just compressed.  


More of the same inside here. 
No Value added info....