1. Open the file you want to place crops marks in.

2. Go ahead and select the Preview mode located at the bottom on your tool bar.

3. Draw a box that snaps into place of your document size area.

4. Under File, Export your file as a pdf.

5. In the Export Pdf settings, select Crop Marks. Here you can change the strok weight if you wish.

6. Now switch to Illustrator and open the pdf file. You see that the crop marks show up. Note: Select the box and copy it. Delete everything but the crop marks. Under File, select Paste in Front. Now all you have is the box and the crop marks.

7. Select all the crop marks and the box.

8. Switch back to InDesign and paste the box and the crop marks.

9. In case they don't snap into place within your document area, zoom in and place the box aligned with your document area.

10. This is how it will look.

11. Under Object, select Ungroup and delete the box leaving only the crop marks behind.

12.  Now you have your crop marks within your InDesign document.

Crop Marks for InDesign CS3. More info.