[Penguin23]

Quite possible. For a foreigner in Singapore, gender is whatever his/her passport says, and transgenders who have undergone bottom surgery would generally be able to state their new gender identity, even though the NRIC equivalent usually shows their original gender. This is the case for Thais and Viets.

I am speaking as someone who is in a serious relationship with a transwoman for the last 3+ years. I met her in a KTV, and she was, for all intents and purposes indistinguishable from a cisgender female. After about 6 months I realized that she never seemed to have menses, so I figured things out from there. I am comfortable with her gender identity, and we are happy together. She has left the KTV life behind, and we live like a normal couple.

My gf has many friends who are transgender, but it is a sad fact that a huge majority underwent Gender Reaffirmation Surgery (GRS) post-completion of puberty so they will never be able to pass off as a cisgender female. Yes, a large majority do sex work to sustain themselves, and also to fund their planned surgeries but their identity as transssexuals usually gets them a very low rate for sexual services.

Fun fact: A transgender woman and a man can be legally married in Singapore under the Women's Charter. And yes, we can apply for an HDB too. Obviously we can never have our own children, but if we adopt then the adopted children can obtain Singapore citizenship just like other couples.

TLDR: The Singapore authorities will never ask for your gender assigned at birth, so the gender as stated in the passport is a prima facie (i.e. always taken at face value and assumed to be true)