I think that the practice of hanging the Singapore flag on HDB balconies or windows during National Day period should be discontinued. I estimate about 20 to 25% of the flats being rented out to or sold to non-citizens (PRs, EPs and work permit holders).
If they really want a National Day festive mood or show, HDB should go to every HDB block roof top and erect a flagpole with the national flag. At least that can show every resident, whether citizen or foreigner, that they're living now under the Singapore flag. It'd make a grand skyline also with so many highrise roof top flags.