It is important to be certain about where that point is, because insufficient speed can earn you a ticket just as excess speed can. GS 20-141 makes it illegal to drive below 40 MPH in a speed zone of 55 MPH. However, if there is no posting of minimum speed, that restriction does not apply.
Under state law, the maximum speed limit is 35 MPH inside municipal corporate limits, and 55 outside corporate limits. DOT can raise or lower limits depending on whether they find that faster is still safe or the statutory limit is too fast, but the limits must be posted.
The municipality may have taken advantage of para (e)
Local authorities, in their respective jurisdictions, may authorize by
ordinance higher speeds or lower speeds than those set out in
subsection (b) upon all streets which are not part of the State
highway system; but no speed so fixed shall authorize a speed in
excess of 55 miles per hour. Speed limits set pursuant to this
subsection shall be effective when appropriate signs giving notice
thereof are erected upon the part of the streets affected.
Or, para (f)
Whenever local authorities within their respective jurisdictions
determine upon the basis of an engineering and traffic investigation
that a higher maximum speed than those set forth in subsection (b) is
reasonable and safe, or that any speed hereinbefore set forth is
greater than is reasonable and safe, under the conditions found to
exist upon any part of a street within the corporate limits of a
municipality and which street is a part of the State highway system
(except those highways designated as part of the interstate highway
system or other controlled-access highway) said local authorities
shall determine and declare a safe and reasonable speed limit. A speed
limit set pursuant to this subsection may not exceed 55 miles per
hour. Limits set pursuant to this subsection shall become effective
when the Department of Transportation has passed a concurring
ordinance and signs are erected giving notice of the authorized speed
When local authorities annex a road on the State highway system, the
speed limit posted on the road at the time the road was annexed shall
remain in effect until both the Department and municipality pass
concurrent ordinances to change the speed limit.
Once you are outside the corporate limits, the corporation has no authority to modify the limits set by the state, and the state limit of 55 is applicable. There is no requirement to the effect that the corporation must tell you that you may now result your regular speed. It would be polite, but not legally required.