This is a patch plugin for an issue with "E-Signature Plugin" not having mce buttons appear in TinyMCE editors when using BGTFW v1 based themes.

bgtfw-v1-e-signature-patch.php

<?php
/**
 * Plugin Name: BGTFW v1 E-Signature Plugin Patch
 * Description: This  is a patch plugin for an issue with "E-Signature Plugin" not having mce buttons appear in TinyMCE editors when using BGTFW v1 based themes.
 * Plugin URI: https://gist.github.com/timelsass/8ad0e7b3b7444b149097ac1ace250a30
 * Author: Tim Elsass
 * Author URI: tim.ph
 */
add_action( 'admin_init', 'bgtfw_v1_e_signature_patch_remove_bgtfw_hook' );
add_action( 'mce_external_plugins', 'bgtfw_v1_e_signature_patch_post_bgtfw' );

/**
 * Apply BGTFW's filter correctly.
 */
function bgtfw_v1_e_signature_patch_post_bgtfw( $plugin_array ) {
	global $pagenow, $boldgrid_theme_framework;

	if ( class_exists( 'Boldgrid_Framework_Editor' ) ) {

		// Access configs for correct paths to files.
		$configs = $boldgrid_theme_framework->get_configs();

		$bgtfw = new Boldgrid_Framework_Editor( $configs );

		$valid_pages = array(
			'customize.php',
			'post.php',
			'post-new.php',
		);
		
		$valid_post_types = array(
			'page',
			'post',
		);
		
		if ( ! empty( $pagenow ) && ! in_array( $pagenow, $valid_pages ) ) {
			return $plugin_array;
		}
		
		// Currently only pages and posts are supported. @since 1.3.1
		if ( 'post.php' === $pagenow || 'post-new.php' === $pagenow ) {
			if ( ! in_array( $bgtfw->get_post_type(), $valid_post_types ) ) {
				return $plugin_array;
			}
		}
		
		$mce_inline_styles = '';
		$mce_inline_styles = apply_filters( 'boldgrid_mce_inline_styles', $mce_inline_styles );
		$mce_inline_styles = apply_filters( 'kirki/global/dynamic_css', $mce_inline_styles );
		
		wp_localize_script( 'mce-view', 'BOLDGRID_THEME_FRAMEWORK',
			array(
				'Editor' => array(
					'mce_inline_styles' => $mce_inline_styles,
				),
				'post_id' => ! empty( $_REQUEST['post'] ) ? $_REQUEST['post'] : null,
			)
		);
		
		$editor_js_file = $configs['framework']['admin_asset_dir'] . 'js/editor.js';
		$plugin_array['boldgrid_theme_framework'] = $editor_js_file;
	}

	return $plugin_array;
}

/**
 * Remove BGTFW v1's faulty code for e-signature plugin compatibility.
 */
function bgtfw_v1_e_signature_patch_remove_bgtfw_hook() {
	global $wp_filter;
	
	$tag = 'mce_external_plugins';
	$class = 'Boldgrid_Framework_Editor';
	$name = 'add_tinymce_plugin';
	$priority = 10;

	if ( ! is_admin() || wp_doing_ajax() ) {
		return false;
	}
	
	// Check that filter exists.
	if ( isset( $wp_filter[ $tag ] ) ) {
		/**
		 * If filter config is an object, means we're using WordPress 4.7+ and the config is no longer
		 * a simple array, and it is an object that implements the ArrayAccess interface.
		 *
		 * To be backwards compatible, we set $callbacks equal to the correct array as a reference (so $wp_filter is updated).
		 *
		 * @see https://make.wordpress.org/core/2016/09/08/wp_hook-next-generation-actions-and-filters/
		 */
		if ( is_object( $wp_filter[ $tag ] ) && isset( $wp_filter[ $tag ]->callbacks ) ) {
			// Create $fob object from filter tag, to use below.
			$fob = $wp_filter[ $tag ];
			$callbacks = &$wp_filter[ $tag ]->callbacks;
		} else {
			$callbacks = &$wp_filter[ $tag ];
		}
		// Exit if there aren't any callbacks for specified priority.
		if ( ! isset( $callbacks[ $priority ] ) || empty( $callbacks[ $priority ] ) ) {
			return false;
		}
		// Loop through each filter for the specified priority, looking for our class & method.
		foreach( ( array ) $callbacks[ $priority ] as $filter_id => $filter ) {
			// Filter should always be an array - array( $this, 'method' ), if not goto next.
			if ( ! isset( $filter['function'] ) || ! is_array( $filter['function'] ) ) {
				continue;
			}
			// If first value in array is not an object, it can't be a class.
			if ( ! is_object( $filter['function'][0] ) ) {
				continue;
			}
			// Method doesn't match the one we're looking for, goto next.
			if ( $filter['function'][1] !== $name ) {
				continue;
			}
			// Callback method matched, so check class.
			if ( get_class( $filter['function'][0] ) === $class ) {
				// WordPress 4.7+ use core remove_filter() since we found the class object.
				if ( isset( $fob ) ) {
					// Handles removing filter, reseting callback priority keys mid-iteration, etc.
					$fob->remove_filter( $tag, $filter['function'], $priority );
				} else {
					// Use legacy removal process (pre 4.7).
					unset( $callbacks[ $priority ][ $filter_id ] );
					// If it was the only filter in that priority, unset that priority.
					if ( empty( $callbacks[ $priority ] ) ) {
						unset( $callbacks[ $priority ] );
					}
					// If the only filter for that tag, set the tag to an empty array.
					if ( empty( $callbacks ) ) {
						$callbacks = array();
					}
					// Remove this filter from merged_filters, which specifies if filters have been sorted.
					unset( $GLOBALS['merged_filters'][ $tag ] );
				}
				return true;
			}
		}
	}

	return false;
}