In general, laudatory words and phrases may be used to promote goods and services, but are not registerable as trademarks.
Slogans are not used to identify the source of a good or service and thus cannot be registered either.
There are exceptions. See European Court of Justice recognizes ‘Vorsprung Durch Technik’ As Distinctive Trademark
The Israel patent office is fairly consistent though.
A range of decisions have recently issued where laudatory marks and slogans have been refused. These include “enjoined in 70+ countries” and “best enjoyed slowly” both filed by Philip Morris Products for cigarettes. The best enjoyed slowly was allowed with a small graphic element and with a disclaimer for the phrase. See Israel TM Application 213403 and 189964).
Orange Brand Services faired little better with “together we can do more”.
However, McDonalds Corporation have managed to register the laudatory slogan “I’m lovin’ it”.
The difference? well the verb to love is not correctly parsed in the present as ‘I am loving’, but rather as ‘I love’. The poor grammar provides an element of distinctiveness beyond the more common dropped g.
Furthermore, the massive usage has created secondary usage in the public.
I find the argument persuasive. The slogan is so well identified with McDonalds, that when it is heard, the listener thinks McDonalds first, and the meaning of the words afterwards.