Same here on my MBP:
Analysis of sampling signpost_notificationd (pid 199) every 1 millisecond
Process: signpost_notificationd [199]
Path: /System/Library/PrivateFrameworks/SignpostNotification.framework/Versions/A/XPC Services/signpost_notificationd.xpc/Contents/MacOS/signpost_notificationd
Load Address: 0x104adc000
Identifier: signpost_notificationd
Version: ???
Code Type: X86-64
Parent Process: launchd [1]
Date/Time: 2018-04-04 11:17:42.005 -0700
Launch Time: 2018-03-30 22:56:16.013 -0700
OS Version: Mac OS X 10.13.4 (17E199)
Report Version: 7
Analysis Tool: /usr/bin/sample
Physical footprint: 1296K
Physical footprint (peak): 1344K
----
Call graph:
2663 Thread_1968 DispatchQueue_11: com.apple.root.default-qos.overcommit (concurrent)
+ 2663 _dispatch_sig_thread (in libdispatch.dylib) + 53 [0x7fff50b8fd10]
+ 2663 _dispatch_sigsuspend (in libdispatch.dylib) + 21 [0x7fff50b8fd25]
+ 2663 __sigsuspend_nocancel (in libsystem_kernel.dylib) + 10 [0x7fff50d0e02a]
2663 Thread_1632769
+ 2663 start_wqthread (in libsystem_pthread.dylib) + 13 [0x7fff50ed4be9]
+ 2663 _pthread_wqthread (in libsystem_pthread.dylib) + 1035 [0x7fff50ed5009]
+ 2663 __workq_kernreturn (in libsystem_kernel.dylib) + 10 [0x7fff50d0e292]
2663 Thread_1632858
2663 start_wqthread (in libsystem_pthread.dylib) + 13 [0x7fff50ed4be9]
2663 _pthread_wqthread (in libsystem_pthread.dylib) + 1035 [0x7fff50ed5009]
2663 __workq_kernreturn (in libsystem_kernel.dylib) + 10 [0x7fff50d0e292]
Total number in stack (recursive counted multiple, when >=5):
Sort by top of stack, same collapsed (when >= 5):
__workq_kernreturn (in libsystem_kernel.dylib) 5326
__sigsuspend_nocancel (in libsystem_kernel.dylib) 2663
Binary Images:
--can be provided if needed.