Speed is relative to wherever the reference point is. If the reference point was an observer and moves at 50 km/s, and the object as a sign is moving at 0 m/s, then from the perspective of the observer, the sign is moving at 50 km/s. The object has no velocity, but moves very fast past the observer. The above answer is meant to make you sound smarter, and does not actually answer the question from your teacher or friend.
Wow, this just reminded me how much I remember from my physics class. But, anywho, velocity takes into account (vector) where as speed does not (scalar). They're used interchangeably in common speech. So, to answer your question, I think: yes.
hmm not really remember cuz long time ago but da speed move like curve when reach speed light, gah anomaly~
Some of the complications arise from the fact that as velocity approaches c, mass increases, which also increases local gravity, which slows down local time (this has actually been demonstrated using atomic clocks in cars on a highway in the US in 90s IIRC) which means velocity is arguably lower (& as mass increases the volume where gravity increases gets larger, as does the dilation of time). So I simplified (because I don't really understand all of it myself) to "funky".