Even Though there is No Official Heterosexual Flag. there are Two Common Flags used to Identify Heterosexual People. First one Containing 3 Stripes of Blue (Male) White (Relationship/Love) Pink (Female).
Second one Is a Black and White Flag containing a Random Disputed amount of Black and White Stripes.
The Black and White Variant was Originally Rumored As an Anti-LGBT Pride Flag and Eventually Become a Unofficial Symbol of Heterosexuality.