Opposition filings and infringement notices
A registered trademark gives you a legal claim. It does not stop someone using the name anyway. Two tools cover most disputes. Opposition stops a third party's application before the mark is registered. An infringement notice asks someone already using the mark to stop. Picking the wrong one is the most common mistake.
Opposition, before the mark exists
In Singapore, a trademark application is examined and then published. Anyone with an interest can oppose it within a two-month window, which can be extended on request. The grounds used most often are similarity to an earlier mark, prior use, and bad faith filings. Opposition is a formal proceeding that runs on registry timelines. Many matters settle during the process, and the squatter withdraws the application and agrees to hand over the name.
The notice and what follows
An infringement notice, sometimes called a cease and desist letter, tells the other party that their use of the mark infringes the registration and asks them to stop. It works well against accidental users. A domain investor or a small operator who picked the name in good faith usually responds. The letter has no force on its own. Against a deliberate squatter it leads to the next stage, a court claim for infringement or passing off. The letter's real value is the record it creates.