xxx = kisses
xox0 = hugs and kisses
They are common symbols in countries where English is the official language. I am a 5th grader who live in US, I use them on e-mails or greeting cards to my friends and families.
結尾既時候佢地會加xxx = regards & tks!
these kind of words is just equal to YOURS FAITHFULLY, or YOURS SINCERELY
When you write a LETTER, you need to have FORMAL WORDING. Thus, the opening of letter is DEAR XXX and the ending YOURS FAITHFULLY
Reversely, when you write a EMAIL, you will only need to have a INFORMAL WORDING. for example; the opening is HI, GUY or just write the name of receiver and the ending is BEST REGARDS or regards.