One example of advertisement in a Cinema is posters in the main area of the cinema however this is commonly used to advertise other upcoming movies which means that it probably wont be effective for a company trying to sell a product also these posters come in different sizes one of which that I have personally seen is a poster that wraps around a Pillar in a Cinema these are quite big but for a it can make the image on the poster look weird so you would have to know what it would look like before hand, there are also your common A4 size posters and A3 size paper posters posters at Cinemas can also, be backlit making it easier to see in the dimly lit areas.
Another form of Advertisement in Cinemas is Cardboard cut outs however these are also commonly used to advertise other upcoming movies meaning these are not going to be as effective for advertising products to frequent Cinema users however if your company is advertising a Movie then this type of advertisement will be effective.
Another form of advertisement is popcorn boxes and drink cups can have advertisement for an upcoming movie on them to try to sell an upcoming movie to frequent Cinema users also, these can be effective because they will be in your hands and within view of your face for a lot of time especially the cup as you will be drinking from it however in the Cinema when viewing the movie it will be dark so it will be hard to see.
One Last example of advertisement in a Cinema and this is the main one is the Adverts that run before the movie these are very strong adverts because according to (http://www.onadvertising.co.uk/cinema-advertising.html) these are the least avoided Advert that is because it is shown just before the movie also these adverts are shown to a captive audience which means that they are more likely to pay attention to the Advert shown before the movie. Another positive of this type of advertisement is that the ad will use the speakers in the Cinema which are quite immersive which means that the companies advert could see very strong Ad recall, also because of cinemas being placed all over the world you can target certain demographics based on the geographical location of the Cinemas that the Advert will show at, also they can target their demographic because they can have their Advert play before certain movies one example for this would be if their Advert is for a Toy or Children's product they could have the Advert play before Movies suited towards Children or if the product is suited towards Adults then you can have the Advert play before a Movie that is more suited towards Adults.