the stamp thing is true
I can say it was the worst nightmare of every hongkongers who are going to China for mongering.
10 years ago the visa for hk and macau people are not the actual red card but a book like a passport.
you got a stamp with the date everytime you are going to China, so your wife can know how many time you went to China, and if you got caught by the police, you got a lovely a red stamp with the word "busted"
all the married men are so happy since the visa change to the red card, easier the cheated their wife
But I'm not sure if got the stamp thing now with the other countries passport.
in Zhuhai area I hear that if you got caught you can either pay 5000rmb (but the price can be different depending on the policemen) or stay 15 days in jail