There are three bands with this name
1. A German hardcore/experimental band
2. An Indonesian metalcore band
3. An English melodic metalcore band

1. Sincerity was a hardcore/experimental band which formed in Sachsenhausen, Germany in 2003
The band's official site is https://www.facebook.com/sincerityhc
They disbanded in April 2013 without making a public announcement.

2. Sincerity is a metalcore band which formed in Bandung, Indonesia in 2009. The band's official site it http://facebook.com/sincerityofficial

3. Sincerity is a melodic metalcore band from Kent, England which formed in early 2011. The band's official site is http://www.facebook.com/sincerityuk
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