CLOCK_SIGNAL constraint XILINX

[rider]

Hi all!

I have a design with combinational clocks. The synthesis report asks
me to use CLOCK_SIGNAL with these signals. However, I have a problem
using this constraint. It can only be used through Verilog/VHDL and
not from constraints editor(Xilinx ISE 5.1). So i am using the
following statement:

//synthesis attribute CLOCK_SIGNAL of J1106 is yes;

However, this doesn't seem to work. Their is still the message in
synthesis report "Please use CLOCK_SIGNAL constraint....". The
hierarchy of my design is as follows:

module DFF_54174.v instantiated in module SHEET3.v as Z158. Module
SHEET3.v instantiated in module DMAB.v [TOP LEVEL] as CIRCUIT3. The
signal to which i want to apply constraint is pin10 of DFF_54174 tied
to J1106 in SHEET3.v. J1106 is a wire in TOP level DMAB.v.

Now is my above constraint statement OK? If yes why is now working?
Where to place this statement? TOP level? or in SHEET3.V or in
DFF_54174.v ? The synthesis report indicates this signal as :
CIRCUIT3_J11061:O ? should i use this instead of J1106? Should i use
quotes around [yes]?

Regards
Rider