Turn signal housings
The 'arrow head' shape is mainly found on newer bikes manufactured since 2006. Commonly used by BMW, KTM, Triumph and Aprilia.
The slightly more 'curved' shape was mainly used on bikes from 2000 to 2012. Commonly used by BMW and Moto Guzzi during this period.
The even more rounded 'bulbous' shape is found only on BMW bikes from 1990 to 2004.