These punctuation marks are called Alamatul Waqf or stopping punctuation.
(م) Meem: When seen, it means you must stop, it is a mandatory stop. Mind you, you will also see a meem After a Noon Sakin or a Tanwin which means that the rule of Iqlab is to be applied. You will see a Baa' after it, if you see no Baa' than there is no Iqlab.
(ج) Jeem: It means you are able to stop if you want.
(لا) Laam Alif: Means to not stop here
(س) ٍُSeen: Means to take a soft/short pause without taking a breath. You would also sometimes see a Seen above a Saad (ص) That means you pronounce the latter a seen instead of Saad, but if it is under the Saad than pronouncing it as a Saad (it's original pronunciation).
(قلي): Means that you can stop or move on, but stopping is more preferred than continuing on.
(صلي): Means you can stop or continue on, but continuing on is more prefered than stopping.
This means you can stop at one of them but not both, so you can stop at (ريب) but not at (فيه), but you can not stop at (ريب) and (فيه) but just at one of them.
Tip: Usually you can look at the back of a Qur'an and you can see the list of the Alamat/Signs.
There is also Alamat in the Indian Script, they have most of the above. Here is the rest:
(ز) Zai: al-waqf al-mujawwaz, means that you can stop, but the better choice is not to stop.
(ص) Saad al-waqf al-murathkhas:
means that the statement has not yet been completed at this point but, because the sentence has become long, here is the place to breathe and stop rather than do it elsewhere.
سكته: means one should stop here breaking the sound but not the breath.
Means one must stop a little longer than saktah (pause). But, breath should not break here too.
means that some phoneticians of the Qur'an identify a stop here while others do not.
This word is 'qif which means 'stop' and it is inserted where the reader may possibly think that a stop was not correct there.
Read More Here.