So, I used tips from the link shared in @ariehen 's reply i.e. About finding Bugs, and finally found the plugin which is responsible for this Heart Break Symbol. This is Obsidian Card Note Plugin.
For this, I moved all the plugin folders from .obsidian/plugins to a separate folder and then reloaded the app. The by moving one plugin folder at a time and reloading the app, I finally found Obsidian Card Note Plugin. This plugin is using the 
symbol by default. Phew… 
BTW, its quite a useful plugin, especially if you use your notes references in Canvas or ExcaliDraw …