Being bicurious is not typically a sexual orientation like bisexuality. You can consider bicurious people as those who travel from one end of heterosexuality to the other end of bisexuality. Unlike bisexuals, it is very complicated to identify a bicurious person, and it is also hard to keep that person under one roof. Simply, any person may get confused while trying to label a bicurious person. They may be straight or maybe bisexual and this confusing state continues forever if you don't know how to identify them. Hence, a few signs may make your task easy to understand, comprehend and perceive a bicurious person.
For starters, it is always better to consider a bicurious person as a heterosexual who is interested in exploring a hidden side of his/her bisexuality. The exploration could be completely physical and sometimes emotional. Most bicurious people try to explore sexually to know whether they can feel the vibe of a fellow same-sex person. Bi-curiosity is all about curiousness and most of the time, it stops at just being curious instead of being experimental. So, altogether, never expect a bicurious person as bisexual.
We, humans, work on signs only when we get confused in recognizing a particular person or a situation. If someone who tags himself/herself as heterosexual, approaches you repeatedly even though that person knows you belong to the queer community then you need to make sure whether that person is interested in you or just being curious to know you inside out. Hence, you need to eliminate the unnecessary choices to get partial clarity.
Homophobic or queerphobic folks can never be bicurious. They are judgmental about the whole queer community and they keep expressing their suppressing views. But some people pretend to be homophobic just to satisfy typical societal norms. Mostly a homophobic person can never express curiosity towards same-sex encounters. But if a person supports you privately and expresses his slur on queer people in public, he could be curious towards you but it's better not to entertain such double standards people. So, you need to eliminate this choice for sure.
Next comes, the queer allies. These sweet heterosexuals bring true power to the queer community by giving their immense support and by lending their shoulders to queer people to lean on. They never judge, and they are quite flexible in exploring their sexual fluidity. So, there are high chances for queer allies to become curious to know how a queer orientation works in society be it homosexuality, bisexuality, transsexuality, or asexuality. If a known queer ally of yours approaches you with an underlying intention of knowing you completely and getting along with you in every possible way, then yeah get ready to deal with a bicurious queer ally.