As a Singapore based *G, I can confirm that Tactical Pens are allowed, though sometimes you may need to show that it is a pen. (Uncapping it if it is not a push button type) There is an active interest by a local airline flight crews to purchase them.
I have more problems with Hong Kong when I bring 100 China Made Metal Body pens as they want to inspect why I bring so many metal tubes.
(Disclaimer, I am a part owner of a business which sells and distribute Tactical Pens in Singapore)