One time, our party of "X+1" saw a sign like that and we split-up three-to-a-table and kept table-hopping. One of us then picked-up the three bills at the end of the meal. The 'tresses were amused and they were individually tipped well - when we were seated - and nothing but the bill was paid when we left. The management believed we left no "tips".
Tips, properly, are given in anticipation of good service so that, therefore, the tippee is indebted to the tipper for the gift (bribe, if you will) and provides commensurate service - they are fulfilling YOUR expectations rather than hoping you'll fulfill THEIRS with a good gratuity afterward.
Gratuities are customarily given after the service is rendered and are, in reality, more "frustrating" for the serviceperson because they then have to work (provide 'worthy' service) toward an intangible/unquantifiable (sometimes nonexistent) goal (the amount of the tip).
You will find (if you seriously ask them) that most servicepeople (indeed ANYONE, if you think about it) will provide honest and generous service to someone who has already demonstrated their opinion that they value what is being done for them; compared to someone doing a good job and getting nothing in return.
We are always well-attended when we go out to eat. It does put the onus on the tipper the first time it is done (if you tip well can you then expect good service?) but, if you frequent the same establishment and get to know the personnel, it ends-up being a better relationship.
When my friends an I go out, adding gratuity to the check is cheating the servers. If the service is just acceptable we tip pretty well, usually more than the appended gratuity would be...