Install a support, tie it in, grow it until you see flowers and can decide if it is one you want to have.

If you are back East, long-stemmed Rosa multiflora is a pernicious weed in many places. Among common roses it is pretty distinctive in flower, making identification comparatively quick and easy.

Another key character is that it produces feathery or frond-like bits from its stems, near its leaf bases. But many desirable garden hybrids with this species in their parentage also display this feature.

Wait until it blooms, don't prune it until afterwards. If the flower is dark red and is a single form (less than 12 petals), then the rose is probably Dr. Huey, which is a once-blooming climber that is commonly used as rootstock. If it is Dr. Huey, there was some other grafted variety originally planted, but that rose died off, and Dr. Huey "suckered" (began to grow). It happens with roses grafted on Dr. Huey. If it is Huey, you can decide to keep it, but around here, it is very prone to blackspot and powdery mildew. But, you won't know what you have until it blooms and you can describe the blooms (size, color, number of petals, fragrance). Photos would be helpful.

Many 'Dr. Huey' here also show mosaic patterns.

bboy, surprisingly, they don't here. In fact, the ones here (and in Philly near my Mom) look like world beaters in the late spring, all green and bloomy and healthy. You would think Dr. Huey was the greatest plant ever. Don't stick around after bloom time though, the rattiest, mildewiest beast ever.