Three little symbols, three different meanings — and using the wrong one can actually hurt you.
™ — trademark (goods)
Use it on a brand name or logo for products to claim rights. You can use ™ anytime, with no registration — it signals "we're treating this as our mark." It gives notice, but the legal weight comes from actual use, not the symbol.
℠ — service mark (services)
The same idea as ™, but for services rather than goods (a consulting firm, a repair shop). Also usable without registration. In practice many businesses just use ™ for both; ℠ is the technically precise choice for services.
® — registered (federal registration required)
The circle-R is the important one. You may only use ® once the USPTO has actually registered your mark — not while your application is merely pending. Using ® before registration is improper and, if done knowingly, can jeopardize your rights or your application.
Why ® is worth the wait
® gives legal notice nationwide, unlocks statutory damages, and lets you use the federal courts. The moment your registration issues, start using it — it's one of the few pieces of free leverage trademark law hands you.