Need help identifying window manufacturer
If there are no redeemable markings or stickers, you may need to rely on the physical appearance of the window frames to help identify the manufacturer. Key identifiers that would help include (but not limited to):


Whether the window is interior or exterior glazed.
Whether the window is a slider, casement, awning, or fixed/picture unit (take clear pictures of the hardware as those can be useful identifiers, especially for manufacturers who use custom or specialized hardware for certain window types. Hardware can include casement/awning hinges or crank-out arms, slider rollers or locks, and/or vertical slider spring balances or locks).
If the interior jamb is attached to the frame or integrated as a monolithic unit (same with exterior options such as a brickmould or nailing flange).
The window material is PVC; PVC w/ aluminum cladding; aluminum; wood w/ aluminum cladding; fibreglass; or other.
The interior and/or exterior finishes are material, painted, laminated, cladded, etc.


From there, take pictures of your windows and talk with local window suppliers or sellers (in person, over the phone, or email) within your area and ask if the windows look familiar and match existing window series. While this method may be more time consuming, you may be able to increase your odds of finding the original manufacturer through local parties identifying your windows. This method may also help if your series of windows are discontinued and cannot be found online anymore.