For the preservation of signature photos, it is better to use plastic film than to mount them with photo frames. There are two main reasons:

1. The use of plastic film can protect the signature photo from high temperature or humid environment, keep it dry for a long time and avoid mildew. However, the signature photo in the photo frame may be damp or moldy due to environmental factors, and the edge of the photo frame may also cause some wear and tear to the signature photo.

2. The plastic film can keep the signature photo clear, not affected by the color and brightness of the photo frame, so that it can keep its original color. After framing, the signature photo may not be clear enough due to the color or light of the photo frame.

To sum up, it is more appropriate to save the signature photo with plastic film.