All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
A husband should not kiss his wife when other people can see them, or in a place where it is most likely that other people may see them; because bashfulness in one of the traits of faith, as reported from the Prophet by Al-Bukhari and Muslim . Therefore, one should observe the Islamic etiquette when enjoying his wife.
Ibn Qudaamah [from the Hanbali school of jurisprudence] said: ‘A husband should not have intercourse with his wife when it is possible for someone else to see them or to hear their noise when copulating. Also, he should not kiss her or touch her in front of the people. Imaam Ahmad said: "For me, it is desirable that he should conceal all of this (i.e. do this in privacy only)."’
Therefore, if a husband tries to kiss his wife in front of the people, she is obliged to advise him and remind him to fear Allaah and to avoid doing so, because this public kissing is the practice of the disbelievers who have no honour nor dignity nor bashfulness.
However, if the married partners are sure that nobody at all could see them, then there is no harm for a husband to kiss his wife.
Allaah Knows best.