Alternatives that will definitely work in this design are BC548C and BC547C, but almost any high gain NPN silicon transistor will work if you get the pins the right way round. The 'C' suffix indicates the high gain grouping and that is the best to use in this design. The schematic symbol will often have a circle drawn around it, especially if it is a higher power transistor. The leads left to right are collector, base, emitter. The rear of the transistor is rounded. This case type is designated TO-92. Not all TO-92 cased transistors have the same C-B-E pin-out.
Fairchild BC549C Data Sheet