As-Salaam alaikum,
In diligently examining the Holy Qur'an and Sunnat-Nabi, Sallallahu alaihi Wasallam, one would certainly come to the conclusion that the following are some of the Signs of Sincere Muslims in this world:--

(1) They speak the truth at all times
(2) They are good listeners
(3) They hardly take offense
(4) They are quick to forgive
(5) They are relaible
(6) They are supportive
(7) They have appetite for prayers and fasting
(8) They rely on the Word of Allah, the Holy Qur'an
(9) The more Allah lifts them up, the more they become humble
(10) They hardly defend themselves
(11) They are quick to repent
(12) They seek peace and pursue it
(13) They love people and they are compassionate
(14) They have a lot of patience and they are not short tempered
(15) They fear Allah Ta'ala.

Let us ask ourselves, are we sincere Muslims? I pray that Almighty Allah gives us the Grace to identify and work on our weak areas, ameen.
Best Wishes.