ALL WAITING SEATS ARE RESERVED FOR CUTTING CUSTOMERS ONLY . SORRY FOR INCONVENIENCE CAUSED.
What is problematic with this sentence?
1.) Syntactical structure.
2.) Meaning of the sentence
Syntactical structure: Ok, I know this is not a syntax module but still I have this urge to want to point this out. Look at the second clause. The DP inconvenience lacks a specifier D. Which lexical items or should I say grammatical items could take the position of this specifier D?
Response: Any ,the ,this. So we could say: Sorry for this /the /any inconvenience caused.
Meaning of the sentence:
I am very disturbed by this. Wait, before going any further, I must inform you all that this notice was taken from QB house. Just for your information if you loiter around malls very often. This QB house is like the many hair salons that you across this island. You patronize this salon to get a haircut because it is cheap (10 bucks) and efficient. When I say efficient, I mean to say that your new hairdo is ready in 10 minutes! Whether it looks good or not is a different issue. As the saying goes, you get what you pay for, so don’t expect yourself to get an extremely fashionable hairdo if you’re paying 10 dollars. Otherwise, the service is reasonable. Ok, away from the digression.
What is so bothersome about this sentence is the use of word cutting .
Checking the definition of cutting: we get:
Our Cambridge dictionary tells us that cutting can be used as an adjective, verb, noun. I will just extract the definition for cutting as an adj.
cutting adjective
/ˈkʌt.ɪŋ/ /ˈkʌt ̬-/ adj
unkind and intending to upset someone
a cutting remark/comment
He can be very cutting when he chooses to be!

.The reason why I have selected the definition of cutting as an adjective is because looking at the sentence, intuition tells us that the word cutting seems to modify the DP customers. Also, based on the context, a hair salon, we infer from the text there is this connection between the word cutting and customers to mean “customers wanting to have their hair cut” , albeit the awkward structure of the sentence.
The MW dictionnaire defines cutting as such
Main Entry: 2cutting
Function: adjective
Date: 15th century
1 : given to or designed for cutting; especially : SHARP, EDGED
2 : marked by sharp piercing cold
3 : inclined or likely to wound the feelings of others especially because of a ruthless incisiveness
4 : INTENSE, PIERCING
— cut•ting•ly \-tiŋ-lē\ adverb
More data on cutting:
The concordance sampler shows no instance of cutting primed to a living being.
So sentences like:
1.) The cutting boys are waiting to have their hair cut.
2.) The cutting customers are unhappy with the service.
A better suggestion to this would have been : All waiting seats are reserved for customers only. The cutting is redundant in this instance. Attention to all shop owners : Please be mindful of your English when you post up a sign.