 a sentence I cannot understand
The little girl loved to get letters from her mommy. They always told her how special she was and had lots of XXXXs and OOOOs on them.
What does the XXXXs and OOOOs mean? Here is the context:
The Magic Jar Years
One day a mother brought home a small jar and gave it to her little girl on her birthday. She told her little girl that the jar was magic, and she could write to her mommy about anything in the world, put it in the jar, and later, in its place, there would be a note for her. Soon the jar became a special part of their lives.
The little girl loved to get letters from her mommy. They always told her how special she was and had lots of XXXXs and OOOOs on them. Often there were reminders of something special they had planned together the next day, or a good luck letter if there was a dance recital coming up. Sometimes, too, there would be a little gift in the jar and a note telling her how proud her mommy was of her. She kept all of her mommy's letters in a pretty box by her bed.
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