As seen in Ramayan, Hanuman is seen as true devotee, as he serves Shri Ram's feet with a loving heart. I will share my interpretation of  particular events when He had smeared sindoor over his body, and one time, teared His chest to show Sri Rama Sita seated in His heart.
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Sindoor is a bright red powder, which can spread across the place of contact, and afterwards stain it! If sindoor is dropped in water, the water will be immersed in it. One main principle of this is!! Sindoor is always applied..

Sindoor is that of devotion itself! It spreads through the body and leaves a positive impression on the soul. Even a little pinch of shraddha and devotion, the entire soul will be immersed in it. Lastly, one can apply love and devotion. Shri Hanuman had immersed himself in His devotion for His Bhagwan Ram. And, he tears His chest to teach us that we should register our God in our heart.  This is more valuable than a necklace of 108 pearls.