Sit down, put your head in between your knees and start yawning. Yawning makes your eyes water and whenever someone taps on the back of your head, put your face up and they will see that your eyes are watery. You can either start crying after that or you can act as if nothing happened, which will make the other person grow more curious. Fake crying does not only mean that you use your voice to show others that you have been crying; the best way to get the attention of others is by showing them that nothing has happened, which makes them grow curious.
If you want big tears in your eyes, glycerine is the solution to all your problems. Simply apply a small amount right under your eyes and they will turn into waterfalls. It might even be hard for you to stop in this case, so you should be prepared for it. With so many tears flowing down your cheeks, you can’t tell people that you are going through nothing. In this case, you will have to start ignoring others so that they know that you are crying and something is most definitely wrong.
The sounds you make matter a lot. Sniffing, in most cases, is perfect. Simply make a few sniffing sounds every now and then and people will notice how you are crying. However, this sound is not loud enough and might not get the attention of many around you. Therefore, make sure that you do this when others are sitting closer to you and you are sure that they can hear you.
Another sound which you can make is that of usual crying. Do not sound too artificial - screaming never gets the job done. Be soft, but try to make your mark on others. Emit sounds which you would in case you are hurt. It helps gain the attention of people around you.