if it's an Si it will have a sun/moon roof and multiport fuel injection, if it's a dx it'll only be dual point fuel injection, if it's an hf it'll have multiport fuel injection and no moon roof. well at least this holds true for 90-91. The Si will also have the letter CRX embossed in the door panels. the Si is a 1.6 ltr, the dx is a 1.5 ltr.
from the refernce material
88-91 CRX - Standard & HF ED8, Si ED9
the crx's were either hf,dx,si