The first signs of a blocked toilet are usually indicated by the slow draining of the water from the toilet bowl after flushing. Often, it will take significantly longer than usual for the water level to drop, and the level may even drop lower than usual in the bowl, which is caused by the vacuum effect of a blocked drain.
A sure way of knowing that your toilet is blocked is if you flush your toilet and the bowl fills up with water, there is not a more certain sign of a blocked toilet than a full bowl after flushing. Excess toilet paper or something foreign being flushed down the toilet like a toilet is usually the cause. Whenever this happens it usually means the blockage is contained to the toilet trap and the remainder of the sewer drains are not affected and working fine.
A gurgling sound coming from other fixtures in your home and bathroom may also be another sign that the toilet may be blocked. A blocked drain changes the liquid-to-air ratios within the drain, causing sewer gases to escape through water seals and vents within the sewer system.