IDA .sig file doesn't work when target is 16 bits?

[ycloud]

I use IDA to disassemble a NE file.
And this 16 bits target used a 16 bits obj, I am sure for this.
But when I make a .sig file and apply, no functions matched.

IDA .sig works fine when tartget is 32 bits.
Does IDA .sig file works file when target is 16 bits? Only for 32 bits target?
Has someone successed in applying .sig to 16 bits target and
several functions matched?
//thanks