Cat on the Roof
Hitchcock uses a black cat on the roof to cut away to during the cat burglar's robberies. It is a symbol that this thief is allusive and without an identity. And every time we see the cat we know that they next morning there will be a report of jewels being stolen. Thus we as the audience can get ahead of the plot.
On an Island
Robie swims out to talk with Danielle on a floating platform outside the hotel. It is a symbol of the secrecy of their relationship. And when Frances sees him speaking with her she swims out to see what all of the fuss is about.
Out of the Flowers
Hitchcock shows a close up of flowers in a market before zooming out where we can see Robie approaching. This symbolizes that Robie is looking for something and hasn't a clue where to start as he has never met the man that has asked him to come to this public place for a first time encounter.
Angry Cook
Robie goes into the restaurant in Nice to find the staff is all ready to have a go at him. One cook holds a frying pan in his hand and is a symbol of Robie's reputation to the men who he once served with. That they do not hold him in such high esteem as he is now living the high life and they are still grunting away trying to scrape by.
Masquerade
Robie and Frances attend a Masquerade ball hosted by wealthy french aristocrats in order to catch the real cat burglar. The masquerade is a symbol that the identity of everyone is in question. Thus anyone could be a suspect in the jewel robbery. So, Robie and Frances will have to keep their eyes open.