Assuming you are using the sample code from here:
http://www.smartmenus.org/docs/#menu-toggle-button
for example, you could achieve it by making the following changes:
HTML:
<!-- Mobile menu toggle button (hamburger/x icon) -->
<input id="main-menu-state" type="checkbox" />
<label class="main-menu-btn" for="main-menu-state">
<span class="main-menu-btn-icon"></span> Toggle main menu visibility
</label>
<h3 class="main-menu-heading">MENU</h3>
<!-- Sample menu definition -->
<ul id="main-menu" class="sm sm-blue"> ...
CSS:
#main-menu {
clear: both;
}
.main-menu-heading {
/* style the MENU text as you like here */
}
@media (min-width: 768px) {
.main-menu-heading {
display: none;
}
}
.main-menu-btn {
float: right;
/* ... the declarations from the Docs */
}
/*... the rest of the rules from the Docs */
Hope it’s clear enough. Cheers!