Upvote:3
I find it very hard to find clear information on this, but as far as I can tell, this page is where limitations to the passport would be posted by the state that issues the passport (in this case Singapore). There are general limitation some countries issue on their citizens, banning them from travelling to certain other countries. Reasons might be safety or might be of political or religious nature. Singapore does not have such restrictions, hence the page is generally empty.
For illustration, here are some passports from other countries with similar entries: