Snap off a leaf, or this time of year, a small branch. If you see a milky exudate, it's norway. Number of lobes on the leaf (norways have more) and shape of buds (sharp=sugar) are also ways to tell, but you're going to have a guide to start with if you really want to understand the differences. What other trees are used as street trees? Start naming them, yep, it's used. The most common Acer species are going to be A. saccharum and cultivars (I'll include some of the less common forms and sub-species here), A. rubrum and cultivars, A. x freemanii and cultivars, and I'm willing to bet there are still going to to be a lot of A. saccharinum around. Less common are going to be the smaller growing trees, A. griseum, A. triflorum, A. ginnala. You may even see a few A. negundo, as unappetizing as that sounds, but in the end, if it's conceivable it could be grown in the area, there's going to be a few of them arouund. Some of the best street trees (Eucommia ulmoides, Corylus colurna) are rarely used because of recognition factors, and many are overused because of recognition factors (Acer). Visit a few local nurseries or contact the forestry department. If you life in a suburb, check with that town/municipality as well as some of the specifics may change with the jurisdiction.

"A pic" is not enough, white mulberries are polymorphic. And weedy. That's why people ask about them repeatedly: they don't recognize one of the many different leaf shapes they produce, and they pop up all over.

Might be a flowering pear - do you have it growing or did you see it or is this a photo of a plant you saw elsewhere? try this link http://www.mailordertrees.co.uk/Pyrus+'Beurre+Hardy'+(Beurre+Hardy+Pear+Tree)/0_caaa100_caaa156/PRAA279.htm

Can't see any picture