Special characters in R-graphics

Question

I have a code in which I use

plot(1, 1, type="s", ylab="log ℓ") 

which is equivalent

 plot(1, 1, type="s", ylab="log \u2113") 

creates a nice oblique l representing probability in the y-axis .

Why l (\u2112) main script version l (\u2112) give me only a field instead of L?

I am running R on a Mac.