Quoted from the Michel Catalog (period of inflation): "Stamps without a watermark are neither inferior nor superior". The watermark 1 is difficult to see on many stamps in 1921, one reason for the introduction of the new watermark grid 2. After several years of work, the wire mesh had worn out and was then consequently replaced.
The condition of this stamp -- heavy postmark, dirty stamp -- and the natural lightness of the watermarks on these issues makes seeing the watermark difficult. I haven't seen anything in the photos. If it's not visible with watermark fluid, you may need to do some combo of watermark fluid + backlighting, or try another method such as a watermark detector or a photo negative scan.